Update:
It was the amp. After checking all connections and trying unsuccessfully to play with positioning and with the amp's EQ, I gave my local dealer a call and they graciously allowed me to borrow their MA352. They also made me borrow a power conditioner promising it would make a difference. Coincidentally, they had a pair of 702 S2 driven by a 120W Rotel amp, so I got to audition the speakers there, and they sounded glorious. So this is what I did when I got back home:
- Added the power conditioner to the MA252+702s: sound was still anemic at low volumes, fatiguing at higher ones. Dare I say no difference at all.
- Hooked up the MA352 with power conditioner (PC+MA352+702s): massive, immediately noticeable difference. Speakers came to life and all my issues with them resolved completely. Sound is big even at lower volumes, tones have texture throughout the spectrum, no instrument is left behind, bass is very present, fast, impactful, on your face but not boomy or overrepresented. Sound is natural and emotionally engaging, exciting. This is exactly what I was hoping to achieve with the speaker upgrade. Big smile on my face again. I already know I've hit home and this is likely my end-game system. And this before even playing with EQ, biwiring, room treatment, positioning, etc. Heaven!
3. Removed the power conditioner from the chain: this one was trickier. Multiple back and forths and testing multiple songs. If there is an improvement, it is subtle and barely noticed on A/B comparisons. Next step is blind tests which I will do later today.
4. Finally, and just out of curiosity, I tried the 683s with the MA352: this was a hard comparison as it had been at least a day since I last listened to the 683s, but wow they sound great. Yes, the 702s are better at everything, but if I couldn't afford them, the 683s would definitely do. Does the MA352 drive them better than the 252? Possibly, but if it does, it's not by a lot.
I am still getting a sub (used REL S5/SHO), so I will report back on how much it contributes, but I can tell you, now with the MA352 I feel no need for a sub. Maybe that will change when I try one, but if not, the REL will be a great addition to my secondary system/home theater.
I just don't understand why B&W would rate this speaker 30-300W when even 100W were not enough to drive it properly, and when they recommend themselves using at least half of the maximum power. I learned than an amp wattage is not just how loud it can get, but that it affects the quality of the sound even at lower volumes when output wattage is waaaay below the max.
I'm so grateful for everyone's input, and special kudos to @erik_squires @ditusa @samac @mofojo @jpconer @styleman @sandthemall @dinov @steve59 for getting it right.
For anyone who's interested, here are a few songs I thought were useful during all my tests (particularly the first 30-60 seconds of each).
- Lithium (Nirvana) for thar punchy drum kick that comes in with the highhat
- Better living through chemistry (QOTSA) for the realism of the initial percussion followed by the broad, bass rich distorted guitar that fills the whole room
- Gagging Order (Radiohead) good mids and highs from a clean, sweet acoustic guitar
- In the cold, cold night (White Stripes) for separation and balance of instruments and the soul shaking, precise bass line
- Acid Rain (Liquid Tension Experiment): for a busy, distorded, very stereo, complex analog metal song with challenging separation
- Twentysomething (Jamie Cullum): nice acoustics that allows you to listen to piano and vocals before introducing punchy drums and bass
Thanks to everyone who contributed. I hope others also find this thread helpful as I'm sure I wasn't the only one unknowingly underpowering my speakers.
Daniel