@Beetlemania, That would depend on the loudspeakers and room. 85 dB is rather a low bar. Much music is intended for much greater peaks. At this level I think we can reasonably expect a lot more. I would really like to be able to achieve about 105 dB peaks on symphonic crescendos. Since ultimate volume levels are not that high a priority for me, I settle for less. I think that compromise might be the weakest part of my system, but I’m OK with it. Though I haven’t measured it, I suspect I can achieve somewhere between 95 dB and 100 dB peaks.
But, that’s not the point. It’s about providing the least distorted, clean power into the actual load at hand. If I recall correctly, your running Thiel CS 2.4’s? If that’s the case, I’d suggest a minimum of 400 Watts into 2 Ohms per channel. Preferably twice that. That might sound like an outrageous amount of Watts, but that minimum can be had with a true high current 100 Watt rated into 8 Ohms per channel amplifier.
If your enjoying your system with less than that, just imagine what it might sound with appropriate power into the actual impedance of your own CS 2.4s!
As to why JA might suggest a "... good 4 Ohm - rated amp..." I would offer because sub 4 Ohm loads are unusual, amps are rarely rated as such, perhaps due to the fact that way back when tubes ruled the day, very,very few amps had less than a 4 Ohm tap.
As for the numbers, if they can provide guidance, why not? Would you prefer that I just shoot off !@#$ from my hip or some other part of my anatomy? Despite all the guru mysticism marketing BS in audio, these are still exercises in engineering.