Well,
Goldmund, FM Acoustics, Tube Reaearch Labs, Sovereign Audio, Tidal Audio and Krell are not likely candidates in this system because I plan to use these amplifiers in my other systems and want something different in this system.
I have heard both the darTZeels and the Soulutions with the Q5. Both combinations sounded stunning but in very different ways. Constellation Audio is now the name on the lips of everyone who has heard them as something new and outstanding. Jeff Rowland's 625 is also getting great feedback and I can imagine the 925 being even better. The Boulder 3050 is even faster, less distorted and more powerful than their 2050. That should be great. The Gryphons (Mephisto Solo and Gryphon Solo) are interesting but last on the list at the moment because the Gryphons I have heard were a little on the warm/slow/mellow side. However this can of course have been a speaker issue. The Colosseum Solo is from their feedback faster and more neutral than the older models. That is why I mentioned them.
The list could be extended to include a pair of internally bridged Burmester 909 Mk.V, a pair of Mark Levinson No.33 (don't want the No.53), a pair of Spectral Audio DMA-360 Series 2, Edge NL Reference, Pass Labs XS-300, Halcro dm88 and tube alternatives like the Conrad Johnson ART, Audio Research Ref. 750, VTL Siegfried Series 2, Jadis JA-800, Octave Research Jubilee, Joule Electra VZN-350 Destiny, CAT JL-3 Statement or Atma-Sphere MA-3, but I need to consider how to combine with the Dynaudio Arbiter and the Q7s in a way that matches well and bring out the sound I am looking for. I think Burmester is too warm, Spectral too thin, the Mark Levinsons too grainy, the earlier Pass Labs too warm, Edge as a company too uncertain future after Tom Maker left, Halcro too thin and all these tube amplifiers lacking a little bit in resolution compared to what at least the Magico Q5 can deliver with the most resolving SS amplifiers of today.
Smaller tube amplifiers like LAMM, Kondo, Wavac is out of the question. I have an addiction what a lot of power does to the sound and could never live without it even with high sensitivity speakers like the Q7.
Less known SS-amplifiers like Ypsilon, Master Audio Systems, Vitus Audio, GamuT Audio (with new designers after Ole Lund Christensen left), BAlabo, Technical Brain and Analog Domain I know too little about to really be able to consider.