Since I would have wanted to see this list before I went on my amp quest (I'm still on it), I'll post my updated list...a year later from the last list.
If anyone is driving Zu Druid 6s or Zu Soul Supremes, here is my prioritized/ranked list. I would expect this list to be the same for Definition 4s or Druid 5s, although I don't own either of those two sets of speakers--but they share enough DNA with my 2 sets that I would predict their alignment.
Here’s my stack rank of amps to date, from best match-up to not-as-phenomenal:
1. Decware Taboo III and Atma-Sphere MP-1 (HUGE surprise to me, but it's incredible)
2. Audion Golden Dream I’s with upgraded caps, Atma-Sphere MP-1
3. Thoress 845 monos, Atma-Sphere MP-1
4. Linear Tube Audio MicroZOTL2, Atma-Sphere MP-1
5. Linear Tube Audio MicroZOTL2, as integrated
-quality gap-
6. Melody 845 integrated
7. Primaluna Dialog Premium HP integrated with great preamp bypassing the PL pre-section, KT150s as output tubes--you can read my posts elsewhere on A-gon on my thoughts on this combo
8 tie. Simaudio Moon i-7 integrated (bypassed with same great pre-amp)--very, very close second and best SS matchup--I was a little surprised this handled all aspects even slightly better than the SIT-2 below (perhaps I shouldn't be surprised since the current version of this amp is like $12K)--maybe the tiniest "etch" and maybe "brightness" on really the top end like trumpets and some female vocals that still probably puts this just barely in 2nd for me; maybe also a slight bit more congestion in complicated passages; shockingly good tube-like midrange for SS
8 tie. Simaudio Moon i-7 integrated (as integrated)--the pre-section in this is stellar, and to be honest, probably not distinguishable when used just as an amp with a really good pre-amp--hence maybe the best value of all I've owned? Still just prefer the PL HP, however
10. First Watt SIT-2 (with same great pre-amp)--very close to #s 7, 8s and 9, but a little too short on decay and "balls" at higher SPL--see my comparisons in other A-gon posts
-quality gap-
11. PL Premium HP integrated with KT150s (as integrated)--very, very good, but I think the pre-amp section could be improved (maybe with a tube-roll?)
-quality gap-
12. PL Premium HP integrated with KT120s (as integrated) -- upgrade to KT150s (better than 88s but not as good as 150s)
13. PL Premium HP integrated with KT88s (as integrated) -- upgrade to KT150s (skip the 120s)
14. McIntosh MHA100 Headphone Amp using it's speaker output--shockingly good--never tried it as just an amp, though--not sure I can bypass the pre-section
15 tie. Transcendent OTL Mini Beast with great pre-amp (would have liked a second to bridge and use as monoblocks--may try to find a second before I sell the first...might move up the list as mono’s)15 tie. Anthem P2 with great pre-amp
17. Primaluna Premium Dialog 2 integrated with KT88s -- probably better if I bypassed it's pre-section but I haven't taken the time to run it that way since finding that combo on it's bigger brother, the HP
18. Nelson Pass Amp Camp amp build--neat little solid state amp, but runs insanely hot and ultimately didn't do it for me
19. Transcendent OTL SE--good but not as ballsy as it's bigger brother the Mini Beast
If anyone is driving Zu Druid 6s or Zu Soul Supremes, here is my prioritized/ranked list. I would expect this list to be the same for Definition 4s or Druid 5s, although I don't own either of those two sets of speakers--but they share enough DNA with my 2 sets that I would predict their alignment.
Here’s my stack rank of amps to date, from best match-up to not-as-phenomenal:
1. Decware Taboo III and Atma-Sphere MP-1 (HUGE surprise to me, but it's incredible)
2. Audion Golden Dream I’s with upgraded caps, Atma-Sphere MP-1
3. Thoress 845 monos, Atma-Sphere MP-1
4. Linear Tube Audio MicroZOTL2, Atma-Sphere MP-1
5. Linear Tube Audio MicroZOTL2, as integrated
-quality gap-
6. Melody 845 integrated
7. Primaluna Dialog Premium HP integrated with great preamp bypassing the PL pre-section, KT150s as output tubes--you can read my posts elsewhere on A-gon on my thoughts on this combo
8 tie. Simaudio Moon i-7 integrated (bypassed with same great pre-amp)--very, very close second and best SS matchup--I was a little surprised this handled all aspects even slightly better than the SIT-2 below (perhaps I shouldn't be surprised since the current version of this amp is like $12K)--maybe the tiniest "etch" and maybe "brightness" on really the top end like trumpets and some female vocals that still probably puts this just barely in 2nd for me; maybe also a slight bit more congestion in complicated passages; shockingly good tube-like midrange for SS
8 tie. Simaudio Moon i-7 integrated (as integrated)--the pre-section in this is stellar, and to be honest, probably not distinguishable when used just as an amp with a really good pre-amp--hence maybe the best value of all I've owned? Still just prefer the PL HP, however
10. First Watt SIT-2 (with same great pre-amp)--very close to #s 7, 8s and 9, but a little too short on decay and "balls" at higher SPL--see my comparisons in other A-gon posts
-quality gap-
11. PL Premium HP integrated with KT150s (as integrated)--very, very good, but I think the pre-amp section could be improved (maybe with a tube-roll?)
-quality gap-
12. PL Premium HP integrated with KT120s (as integrated) -- upgrade to KT150s (better than 88s but not as good as 150s)
13. PL Premium HP integrated with KT88s (as integrated) -- upgrade to KT150s (skip the 120s)
14. McIntosh MHA100 Headphone Amp using it's speaker output--shockingly good--never tried it as just an amp, though--not sure I can bypass the pre-section
15 tie. Transcendent OTL Mini Beast with great pre-amp (would have liked a second to bridge and use as monoblocks--may try to find a second before I sell the first...might move up the list as mono’s)15 tie. Anthem P2 with great pre-amp
17. Primaluna Premium Dialog 2 integrated with KT88s -- probably better if I bypassed it's pre-section but I haven't taken the time to run it that way since finding that combo on it's bigger brother, the HP
18. Nelson Pass Amp Camp amp build--neat little solid state amp, but runs insanely hot and ultimately didn't do it for me
19. Transcendent OTL SE--good but not as ballsy as it's bigger brother the Mini Beast