I own a complete XI Audio combo to listen to my TC. It matches the TC abilities in every ways IMHO.
In overall, it doesn't impose any sound character except those of the recording. I listen to Ben Harper, Taj Mahal and G-Love's music to test soundstage and timbres. These recordings are truly spectacular and remain so with the XI and Abyss combo. As the amp is very resolving and conveys an exemplary soundstage and accurate distinction of instruments, you can hear the acoustic of the room and the sound signature of each instruments : skin of the drums, strings of electric bass, natural reverbs of the slide guitar etc. Pure bliss. More about the soundstage: it is very close to your ears, as if musicians are playing right in front of you. I listened to the TC with the Riviera AIC10. This amp delivers a different scene with more distance between you and the musicians. It's a matter of taste.
The amp delivers a generous and stable amount of energy all across a wide bandwidth, especially in the lows which are Abyss' great specialty. Bass are very very well controlled and impactful. With pop music, dynamics are high and constant but the Amp is never lost, it is always in control. This is a fast amp. The only downside I see is with classical music where recording lacks dynamics most of the time. You will then have to max the volume level to get the thrill with symphonies (but this is my taste. I like to listen to symphonies at high volume levels). In this respect, I would have like a more powerful amp to have some extra juice but for all other genres and recordings, the Formula S is a no brainer.
Adding the Powerman brings a greater separation of instruments and a dead black sound background. The latter is very useful when pairing the Formula S with low sensitive headphones (TC or Susvara) because these types of cans requires to select the High Gain position of the amp which goes along with some hum.
The amp is very sensitive to cables (interconnect and power). You can reach an even greater holographic sound stage and meat in timbres pending the cables. Is it a downside or the character of great amps? Can't say but I see there the resolving asset of the amp, and the opportunity to manage upgrades at my own pace and budget. My next steps consist in cabling everything with JPS Labs cables (I trust these guys) : new RCA Superconductor 4 and Kaptovator. Joe uses Aluminata. I would love to hear the XI's in this config.
Final thoughts: I think that the Formula S and Powerman deliver a very generous amount of joy and pairs wonderfully well with the TC for a reasonable price tag. In the SS amp category, I would probably go for a Headtrip Reference or MassKobo headamp to reach more power (and have my Bank man behind me for the rest of my life). Or a speaker amp which is another option but it requires some care.
Hope that it helps.
