Threshold, Parasound, Pass Labs or Nakamichi?


I have a question regarding my Arcam AVR350 and adding an amp.

I have been a novice hobbyist for over 20 years and have enjoyed the sound of a Nakamichi TA-2A, Adcom GCD-600 and 700, Nakamichi cassette deck and a number of KEF speakers. First and foremost, I am a diehard KEF fan. I have listened to various B&W 800 series, Wilson Audio and KEF Reference and have recently acquired a pair of KEF Reference 205/2s. I initially hooked them up to my little Nakamichi and loved the sound but obviously needed more power and needed to step up.

Unfortunately I also wanted the convenience of running my TV, DVD, and cable as well as my CD player and tape deck. I consider myself an amateur audiophile who loves music first and wants a home theater second. After a year of research, I found the Arcam AVRs were reviewed as the "best" receiver for sound. I acquired the AVR350 and was surprised. This may sound ridiculous but my 50 watt Nak seemed to produce a fuller and more 3 dimensional soundstage than the 120 watt, in stereo, Arcam. I do realize amps drive the speaker and am unsure of how many amps either of these units produce. I love the simplicity of the Arcam, the ease of use and what it does. However, the music sounds very accurate but "flat". The sound is much more 2 dimensional to me. The bass is significantly less pronounced with the Arcam also. I actually enjoyed the sound of my Nak better.

Hence, my question. I am considering purchasing a used amp and hoping to have the convenience of the Arcam pre-amp with the warmth, body, imaging and soundstage of a better amp. Obviously I am a fan of Nelson Pass's technologies and I am sure my dream system would consist of Pass Labs monos. Realistically, I am wondering if anyone would recommend any of the above amps based on their experience. I am considering a Nakamichi PA-7, Threshold s500 or s500e if I can find one, Parasound HCA3500 and I think my budget is still out of reach of a Pass Labs used amp.
spipa
Try the Adcom GFA5500. I've owned 2 & they sounded very good, to me. Around $500.00 used and 200 watts per channel.
This is a realistic match for your Arcam receiver/preamp.
I believe it's a Nelson Pass design, too.
Nelson Pass seemingly had zero to do with my beloved Forte' Model 55 (maybe the last thing Forte' made...well after Pass left Threshold), but I think his vibe is in there anyway as it is a GREAT amp for the $400 I paid last year...maybe I can get Pass to sign it for me or wave his hands over it. Also, Adcom amps have served me well so I can second that suggestion...the Mosfet versions can be killer for the money.
I was using a Nak PA-5 and a PA-5 for many years. Then I purchased a Threshold 400a and swapped it in. I am not familiar with comparable Threshold amps the 400a (updated) totally killed those Nak amps. I now know what the is meant by muddy sound and those Nak amps sounded muddy compared to the 400a.

I was shocked at how much better the 400a sounded.
I like my classe ca-150 quite a bit fwiw. I'd actually like to get another one some day so I can run them bridged. I had an adcom 545 before and the classe was quite a step up; more bass, fuller sound with good detail.
I would first beg/borrow an amplifier from someone and try this to make sure the preamp section is not the culprit.