While I don't use tube amps, the Stereophile impedance curve shown from the review dated Mar 17, 2023 shows what some consider to be an older design when people used tube amps versus more modern designs where impedance curves are both flatter and closer to the 4 ohm mark and can fall under 4 ohms but which may be too demanding for tube designs and even solid state amps regarding heat, clipping, etc.
Personally I think its just a preferred design where low impedance speakers are meant to maximize power output capabilities of well designed amps. A well designed amp with sufficient heat dissipation will likely have no issues.
Your speakers, along with many modern speakers have widely fluctuating impedance values throughout the frequency range with peaks in the lows, mids and highs but also dips to 4 ohms at various points before peaking upwards. So the range can vary from 4 ohms up towards 30 ohms or higher.
Solid state amps are said to be able to output the necessary power for widely fluctuating frequency curves better than tube amps which may like a flatter, less fluctuating curve but the Klipsch are still highly sensitive and easy to drive. I would think the 8 ohm tap will be less restrictive of power output and the few points at 4 ohms isn't enough to over stress the amp. If it sounds better, use it.
The hum might be able to be addressed separately if its an issue. Definitely would call the manufacturer to discuss how to handle.
If your speakers were an 85dB sensitivity speaker then the curve could be more troublesome and the 4 ohm tap a better choice.
As to current output requirements, I think the Raven are pretty good at providing current perhaps from something I read awhile back but the fluctuating impedance might also impact.
Ideally for a tube amp, the impedance curve should be flatter say somewhere between 6 ohms to say 12 ohms as an "example" but few speakers have been designed that way with some still being hard to drive too regarding sensitivity and/or current requirements.
My own speakers, small Audel standmounts have a widely fluctuating impedance reaching a low of 7 ohms in the mids and 5 ohms at the highest frequencies, but reaching a high of around 35 ohms in the mids, probably averaging around 9 to 10 ohms compared to those stated to be 8 ohms. So, while an easy load for an amp, my smallest integrated which had previously played every speaker well, sounded flat, duller on these. I was surprised.
My other two amps with more power and capacitance, more current output too made them come to life with my middle power amp sounding preferred to me. Plenty of power for my needs but it won't compete with the LaScalas as to output.
I drove myself nuts researching impedance curves and no longer worry about it if the system sounds good. Its still important to know what it does to the power output of an amp (lowering output wattage) but it doesn't mean it won't be sufficient for your needs. Perhaps the lowing of power output is too much and you might need a more powerful amp, as in my case but that seems to be about it.
Other views might differ on the engineering design and state a flatter impedance is a better target for a designer to achieve and they wouldn't be wrong, but alot of speakers old or modern still have widely fluctuating impedance along the frequency curve.
You could probably redesign and pay more for a better crossover network resulting in a flatter impedance curve and perhaps a flatter, more linear frequency curve but whether that results in a better sound or not isn't clear, but perhaps it should or at least be truer to the source. Whether you can do this and how much it would cost is a consideration. Any speaker can be tweaked I suppose.
There's also a formula where a speaker shouldn't fall below say 0.8 of the nominal rating, for example an 8 ohm rating shouldn't fall below .8 X 8 ohms or 6.4 ohms even if most nominal ratings don't strictly adhere. So "technically" your Klipsch would be deemed a nominal 5 ohm load accordingly.
Hope this helps or at least explain some things.
