the Cayin will be able to output adequate power but I might be missing out their full potential. 

Bingo!

"Indeed, the Cayin A100T has 8 and 4 Ohm taps, and I’m sure it can drive 86 dB speakers, however, since I couldn’t find information regarding its 4 Ohm output,"

 

Tube amps do not increase power at lower impedances like SS amps do. The output transformer matches the output of the amp to match the speaker’s impedance so it’s still 70wpc out of the 4ohm tap. But this also functions to match the speaker’s impedance to the amp much better. I think 70wpc should be enough if you’re not trying to rock out at 100db. Technic’s recommended power is well within your amps power output. Recommended amplifier power: 40-200 W

It is a good question. If you are in love with the sound of the speakers....

 

Just a quick AI summary of speaker sound and of the amp’s ability to drive them.

 

Quick summary — what the Technics SB-G90M2 soundlike

• Very coherent, focused midrange with excellent imaging thanks to the coaxial (point-source) mid/tweeter—voices and instruments sit very well in the soundstage. (hifiheaven.net, Technics)

• Warm, musical presentation: a little more mid-forward and pleasingly full-bodied than some very “analytical” designs; tonality is aimed at musical engagement rather than bleached neutrality. (LB Tech Reviews, soundstageaccess.com)

• Good low-end extension and punch for a medium-sized floor-stander (specs show ~33–34 Hz extension), so rhythms and basslines have authority. (Upscale Audio, Guitar Chalk)

• Smooth, non-fatiguing treble — detailed but not excessively bright; in direct A/B some listeners find them slightly tamer on the top compared with B&W. (soundstageaccess.com, Witchdoctor)

• Dynamics and build: Technics tuned these with solid cabinet damping and CAE/CAE-style engineering; they respond well to capable amplification and present good dynamic contrast. (Upscale Audio, Witchdoctor)

• Electro-mechanical notes: lowish sensitivity (~86 dB) and 4 Ω nominal impedance — they benefit from a decently powerful, stable amp rather than a tiny bookshelf amp. (Technics, Upscale Audio)

How they compare with other speakers in the same price bracket

(typical competitors: Dynaudio Evoke 50 / 40, Bowers & Wilkins 702/703 series, KEF R7, some models from Focal and Monitor Audio.)

• Versus Dynaudio Evoke (and many neutral-leaning designs)
  Technics = more midrange presence and musical warmth; Dynaudio = a bit leaner/neutral and very transparent. If you want emotional, front-of-stage vocals, Technics often wins; if you want strictly “flat” response and forensic detail, Evoke leans that way. (soundstageaccess.com, Speaker Decision)

• Versus B&W (702/703 series)
  Technics tends to be less bright/forward in the top end and usually smoother on vocals; B&W can sound more “exciting” or forward and more detailed in the presence region, which some listeners call “bright.” If you’re sensitive to treble glare, Technics is friendlier. (soundstageaccess.com, AVForums)

• Versus KEF R7 / point-source rivals
  KEF (and some KEF models) aim for very accurate, neutral imaging from uni-Q drivers; Technics’ coaxial design puts emphasis on mid coherence and a warmer overall presentation. Imaging is excellent on both, but the Technics’ presentation feels richer/denser. (hifiheaven.net, Upscale Audio)

• Value / “what you get”
  Technics offers top-end driver engineering (coaxial/linear-phase concepts), strong cabinet engineering, and a sound tuned for musicality. If you prefer a more relaxed, musical, well-imaged speaker that’s forgiving of poorer recordings, they’re an excellent option. If your preference is ultra-neutral, surgically detailed sound, there are contenders that trade some musical warmth for extra analytical neutrality. (hifiheaven.net, LB Tech Reviews)

Practical tips (amp, room, placement)

• Use a solid amplifier (able to deliver current into 4 Ω and preferably 50–150 W per channel) because sensitivity is modest. (Technics)

• Give some toe-in to taste: small toe-in tightens focus; more straight-on opens the soundstage. Experiment a few feet from the rear wall to get bass balance. (Witchdoctor)

• If your room is very bright, the Technics’ smoother treble means they’ll be more forgiving than some rivals — helpful for everyday listening. (soundstageaccess.com)

Bottom line

If you want musical, midrange-driven speakers with excellent imaging, authoritative bass and a smooth top end, the Technics SB-G90M2 are among the stronger choices in their class. They’re aimed at listeners who prefer engagement and tonal richness over razor-edge neutrality. If your priorities are ultimate analytical detail or highest sensitivity for use with low-powered amps, audition the Dynaudio, B&W, KEF and Focal alternatives to see which tonal balance you prefer. (Technics, soundstageaccess.com, Speaker Decision)

Would you like a short comparison table that lists sensitivity, impedance, typical price and tonal summary for the Technics and 3 nearby competitors (Dynaudio Evoke 50, B&W 702/703, KEF R7)? I can pull the exact specs and prices and lay them out side-by-side.

 

Then I think you should go ahead. They will probably sound great... but at some point you will be able to upgrade your amp... if you want. 

 

 

Yes, the Cayin A-100T (assuming Ultralinear/KT88 mode) can indeed drive the Technics SB-G90M2 speakers, but with some important caveats:

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Cayin A-100T Power Output

• The Cayin A-100T delivers approximately 70 W per channel into 8 Ω in standard operation. (HiFi Engine, Polk Audio Forum)

• Based on tube amplifier behavior with lower impedance loads, it may yield closer to 100–140 W into 4 Ω, according to user estimates. (Audiogon Discussion Forum)

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Technics SB-G90M2 Requirements

• These speakers are 4 Ω nominal impedance, with a sensitivity of 86 dB. (Audiogon Discussion Forum, LB Tech Reviews)

• Manufacturer recommends an amplifier power range of 40–200 W, with 100 W rated and up to 200 W max tolerated. (Technics, Panasonic Help, LB Tech Reviews)

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Real-World Match?

• According to a discussion on Audiogon:

  “Given the low sensitivity and that the speakers probably drop below 4 Ohms at certain points I think you’d be really pushing it with your amp.” (Audiogon Discussion Forum)

• This suggests that while volume levels may reach comfortable listening, the A-100T will be operating near its limits—especially in dynamic passages or in larger rooms.

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Conclusion

Yes, the Cayin A-100T is technically suitable for driving the Technics SB-G90M2. Its output likely meets the lower end of the speaker’s recommended range. However, because the SB-G90M2:

• Has modest sensitivity (86 dB)

• Is a challenging 4 Ω load with possible dips

• Benefits from dynamic headroom in demanding passages

You may experience limited headroom, especially at moderate-to-high listening levels or in large, acoustically lively rooms.

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Recommendations

• If your listening levels are moderate, and you’re in a medium-sized room, the pairing can work well—especially if you value the smooth, musical character of tube amplification.

• But if you frequently listen loud, or your room is large with high ceilings, pairing the SB-G90M2 with a more powerful and more stable solid-state amp (100 W+ into 4 Ω) may be a safer bet.

• Alternatively, consider combining the Cayin with careful placement and room treatment to maximize perceived loudness and bass impact without strain.

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Would you like help identifying solid-state amps in the 100 W+ into 4 Ω range that complement the tonal signature of the Cayin and suit these speakers?

I knew tube amps perform differently when compared to SS, but I didn’t know there wasn’t any increase in the power output when using the 4 ohms tab.

Haven’t heard these speakers but they look really well-built and seem to have the type of sound I would prefer. Unfortunately, they are big and heavy, and wanted to make sure before committing to this purchase.

More of an issue than efficiency actually: Those are 4 ohm nominal impedance speakers, a bad match for a tube amp. 
 

Options for best performance including ability to go loud unfettered:

1)  Higher power Class a/b SS amp with high current delivery capability.   That will be larger, heavier, consume more power to operate and likely cost more.  You might even go class A which magnifies all of the above to achieve a particular SPL. 

 

2)  Class D amp with similar power capabilities.   Stability down to 2 ohm impedance is desirable (in any case for 4 ohm nominal).  Smaller, lighter and more  energy efficient.    These are all I have used now for the last 10 years or so.

 

Tube amps can be a fun alternative but only with the right speakers.   8 ohm nominal impedance or higher.   Sensitivity then comes into play mainly to determine how loud you can go.  
 

Note that tube amps and Class D amps in general tend to soft clip, which is a desirable feature in general.