Threshold, Levinson, Bryston, Krell, ?others? used amps

I had a Mod Squad Quad 405 for over 25 years after having a stock 405 for about 8 years (Mod Squad's Steve McCormack later became McCormack Audio),  a Bryston 8B for several years which was more powerful and slightly more detailed, replaced it with an Edge M6 which was deeper and fuller in the bass and just a little more dynamic and live sounding than the Bryston, and then bought a used pair of Nuforce Reference 9 V3 SE mono amps that are 175 watts/channel.  The Nuforce amps were very detailed, dynamic, with very good bass, with no etch in the highs--a very nice step up in all ways from what I had.  I liked them so much I had TDSS's Bob Smith do the level 3 upgrades to them.  The circuits were not changed, but the power supplies and several other things were--they are now super amps.  I got the Nuforce amps for $1400 used from the original owner.  I've now heard these upgraded amps with 5 totally different but excellent speakers and it was the best each of those owners speakers had ever sounded by a significant margin.  You could buy the amps and later, if you desired, have TDSS do the upgrades when you had more money.  The Nuforce amps already sound very good with a wide variety of speakers--and you'd have a possible end game set of amps if you did the upgrades to them.

Bob

Just becareful buying used ,when it does died ,you have nothing but metal.Which could be an expensive piece of junk.

Krell ksa100. Pure class A. Doubles all the way down 2ohm. Beautiful sound and beautiful looking amp. A true classic. Might be had for 2k if lucky. 

In terms of value, I'd lean towards Bryston because unless you're purchasing something super old you're still going to be covered by the warranty and support.

In terms of the sound character you're looking for, there's a reason Bryston is used in so many professional audio setups.

Lastly, to answer your question about the benefits of the newer Cubed models over the previous generation amplifiers, the Cubed amps have even better detail retrieval, clarity of sound, tonal balance, and noise rejection. They just sound better all around, assuming the sound character described above is what you're looking for. I strongly prefer the Cubed versions over the previous generation.

Never heard a PA7 but knew the PA5... I’d sell the Nak as they still bring in decent cash and spend a little more and look at Pass X250. In my system my X250 disappears or actually my speakers do. I do use a tube preamp but I’d say my preamp is more on the neutral side than tubey or soft,  but that being said my system is smooth, but not slow, bass authority but the Pass doesn’t throw the bottom end in your face but it can slam when needed.

I’ve listened to many McCormacks over the years and the past and current Parasounds and they all are very good and I’d pick those over the Nak but no way would I trade any of these for a Pass... even an older X250. Everyone’s taste and system is different but don’t overlook a Pass. The X250 is probably close to your budget but they don’t show up too often but maybe Reno HiFi has one. Yeah it’s a little old, but built like a tank to last.