I am a big fan of Audio Research. I have an all ARC Reference system and have had 160 monoblocks for well over a year and a 160s for three. There is a lot of synergy with all ARC. You seem to be familiar with the the sonic characteristics. Personally I would not put the PL amp and ARC in the same class. The ARC is far more refined and tuned to reproduce natural music, in all aspects. You have to choose if that is what you want, well, that you value.
The ARC gear presents music with stunning fidelity to the real experience (not exaggerated charactertures), conveying the full rhythm and pace. My speakers are 90db efficient and I operate my ARC amps in triode mode (so, 70wpc)… they will play louder without distortion than I would have thought possible (or desirable in my large room), in the mid 90db range. Typically I listen in the 70db range as it gives me all I need. Occasionally I will listen in the 80’s.
The difference between the mono blocks and stereo version is interesting, and a bit subtle in audition… but very noticeable in ownership. The monos have a wider and deeper sound stage with images set in a larger sound stage… but the individual instruments have a bit less power and immediacy. So, it sounds like, since you like some metal, pop and rock. The stereo version sounds more up your alley… as it will sound like it has more power.
I used to own massive solid state amps. The quest for massive power was always on my mind. But when I switched from solid state to tube amps, that quest for power went away. They have very different strengths and weaknesses. SS tend to sound much better with more power, tubed are far less effected. I mention this as something to think about. I don’t know what it means.
Anyway, after a number of years and thousands of hours with my ARC REF 160 amps… I appreciate them more each day, and particularly paired with the other equipment. You can see my system under my UserID.