I'm not doubting this per se and I see you answer a lot of questions here so I know you know your stuff. What it it that will make a power amp outperform the Rega so notably though? I'm still learning and like the detail behind things. Thanks for your response btw.
I would never say "notably", as 1) Your Rega amp has good specs, 2) it is 4 ohm rated, just not very powerful and 3) you need 2X the power to gain only 3 dB so 160 W vs 300 W can be considered significant, but not really a lot.
The power amps listed can all do at least 300 W into 4 Ohms and that would match well with your speakers based on the recommended 25-180 W. So in terms of power output, the Rega is obviously powerful enough for you based your seating distance and listening habits. Those power amps will just give you some extra reserve that even if not put to use, would allow the amps to relax a little more doing their job.
I have not seen the impedance/phase angle curves of the Classic 30, but if they have low impedance dips, say below 3 Ohms, and especially if it coincidence with some high phase angles, then it is possible that the power amps could in fact give you some noticeable difference/improvements. That's just if.....