Rich; organic true balanced amp w good detail $6k

Suggestions welcomed & appreciated- here are the Criteria:

- fully balanced architecture
- rich, organic sound, extended bass, silky highs, but not at the expense of obscuring detail
- No OTL (too many tubes/heat)
- SS (Class A bias) or tubes OK
- 20-200 wpc ok, the lower the better though all things being equal- well built power supply crucial
- stereo amp easier to put on my Sistrum rack, but mono-bock architecture also considered if better performance
- $6k or less used would be ideal, but would consider up to $8k used if there are no world-beating contenders at the $5k-$6k used price point

Preamp is a modded Sonic Frontiers Line 3- extremely neutral, hence the desire for a richer-sounding amp to balance. High efficiency speakers from Coincident- large open concept room (main floor of house). Re: tubes, have used ARC VT-100 MKIII- good- airy w big soundstage, but meatier mids would be better. Also had Wyetech Topaz 20-watt SET, superb, if slightly lean in the mids (and not fully balanced, but shows you how powerful 20 watts can sound with a well-built power supply) For SS, am considering Pass XA.5 series (they now can run balanced from what I understand?); Clayton Audio M-200 (but unfortunately over the price-range).

Thanks in advance for any suggestions- I have an open mind, so bring it on!
excellent advice- thanks again everyone for the thoughtful and informed responses & recommendations- it's been a LONG time since I started a thread in this forum, and you guys have not let me down- I will look into all of the suggestions- cheers.

Sutts in Toronto
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Tvad- can't argue with you there- only 'Izzy' as I call him will point me to an SET, but then his priorities are only music listening. This system is on my main floor, and is used a lot for movies as well, so a bit more power and a lower noise floor is nice (hence the 'quieter' fully balanced advantage). *All that being said though, if I hear something that really blows me away, I will overlook some of the criteria for the resulting sonic benefit. I am going to investigate these Belles 150A Ref Monos you suggested- are they full enough sounding in the mids?
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Sutts, you are starting to confuse me. It seems like some recommendations are dismissed because they are not balanced (Pass XA-60, Moscode, Manley,etc.). While other single ended amps like the Belles, Lamm and EAR intrigue you. A little help here?
For me, true balanced is a must. My digital front end only outputs balanced, my preamp is fully balanced. Personally, there are enough fully balanced choices out there that I do not see the point in breaking the chain. YMMV.

BTW, the Clayton M-100's that I owned a while back are NOT fully balanced, but do offer balanced inputs, like VAC, EAR and others. The newer M-200's are fully balanced though. If these really interest you, you may try contacting Jonathan at Goldman Audio. He has mentioned to me that he has a demo pair for sale.