Which AMP to Keep ?

I still run PSE Studio V monos in one of y systems. Not well known but good sounding - I'd keep the Studio IV!

From my point of view, I always want to achieve the absolutely best sound quality possible within my financial means. That always means only owning one. So, I would say, sell them all and purchase a better amp.

But beyond that….which sounds best to you? I could not possibly help, since I don’t have your values, system and venue. If you can’t tell the difference, then either just randomly keep one, and figure out the weak points in your system and use proceeds of selling amps to improve the systems overall sound.

Or maybe sound quality is not the top priority to you and someone else will suggest a strategy you like.

I may not be giving a fair comment because i have not heard all of these amplifiers. I was a Sumo Dealer way back and sold a good friend his Polaris. A year or so ago, he gave me that polaris. Being nearly 40 years old, i decided to recap it. I upped the supply caps with about 50% higher uf rating and bypassed each with 10uf mkp. I replaced the polycarb input cap with a polyprop film & silver foil and replaced all the chiclet mylars with film & foils. There were 4 small electrolytic on each board and I replaced 2 with Panasonic FM and the other 2 with Nichicon KZ, Lastly, there is a larger, if I recall correctly 16 or so uf electrolytic on the board. It is need anywhere from 4 mic to 20 mics there and I replaced it with a 10uf mylar. I have a pic or 2 if you are interested.. I have to say, this ended up being very noticeable improvements. Firmer bottom, very smooth midrange and a new refinement on top. I can’t comment on how they compare, but for about $100 in total parts, This has been a welcome improvement on an already decent amplifier

I would definitely keep the Pass and sell the others. 

I liked Sumo amps a great deal in the day. The problem wiht all that vintage gear is that it may be seriously outclassed (or not) today and the power supply components are aging and will need significant maintenance.

The usual neutral, affordable amplifier standby’s are Parasound Halo amps. I’d listen to those and if they don’t sound much better than what you have use your own judgment about what to keep, but plan on recapping now rather than later. Otherwise sell everything and get the smaller 100W/Ch Halo. I forget if it’s the A21 or A23.

Remember that amps are bad when the caps go.  They can have cascading failures that leave you with lumps of metal you can't get fixed, so whichever amp you are keeping, at this age they need to be recapped.