Sounds like there are some people here who are waiting on SW51 and Quicksilver. I thought a quick simple comparison might help. I've lived with SW51 for awhile but just received Quicksilver today. I've listened to it for probably 4-5 hours.
SW51 is known for having a very clean, almost SS-type sound (I quite like this about it). Quicksilver has a little tube bloom and a more liquid, rounded sound (more romantic?).
It's not somewhat blurry, hazy or unfocused like ZDT Jr tends to be. Quicksilver still has great clarity/transparency, which is something that's important to me.
In short, I think they're very complimentary amps. When you want to put on your "serious" hat, it's SW51. When you want a little bit of sexy in your life, Quicksilver has it - without going overboard into warm-goo territory. Far from it. I think Quicksilver struck a nice balance here.
I stay far away from warm, gooey, mushy amps and that's not what tubes are about to me. I am definitely enjoying the Quicksilver, so no worries about gooey. It plays it relatively straight, but just adds a little bloom, a little romance, a little roundness to the presentation.
I've mainly been using the LSA HP-2 so far with the Quicksilver. The bit of bloom helps the otherwise very clean-sounding headphone have a little more character.
I did use the Aeolus a bit, and while it's close, if I had to choose the better amp for the Aeolus *so far*, it would be SW51. The Aeolus has enough flavor to begin with that I prefer to feed it a clean (with tubes) signal. The better amp for the LSA HP-2 (again, *so far*) would be the Quicksilver.
I'm sure further use will deepen my understanding of this amp, but these are my initial knee-jerk reactions after 4-5 hours of listening. Hope they help in some way.
Both amps were fed by a Gungnir Multibit A2 XLR into a Freya+ (in tube mode) to handle the balanced-to-single-ended conversion, then RCA out of Freya to the amps. Source is BNC from pi2AES.