orangecrush, I am using a Tranquility DAC with their less expensive USB cable, PI Audio's better power cable, AQVOX USB power supply, and DIY silver ICs from VHAudio's recipe. I love the DACs NOS 44.1 chip. They say it sounds great with hi-rez, but I could not say from experience.
I was just listening with my 55 Winged C Rectifiers...so it may not be accurate compared to your 57s. Sorry I missed it earlier saying I had 57 Winged C Rectifiers. The other tubes are Amperex OA3, Raytheon OC2, Zaerix labelled PCC88 (looks Russian), JJ6CA7.
In my system they are nice and warm but a little restricted (perhaps a little veiled/less spacious) to me...The bass is a bit flabby with these tubes, but sounds pretty real otherwise. They sound good, and I could likely tube roll to get it sounding really good, but with this set, I hear this tube in my system and my objective is not to be able to identify a tube in the sound. If my system/room were more toward the bright, and less bassy, I think I would still find these a little restricted, but that could be just me.
The Heinz Kauffman labelled Bendix 5Y3GT, after the Winged C's, are sort of like opening a window in a too close room. They are near the bottom of this page here:
http://www.nostubestore.com/search/label/5Y3GT%2F5Y3WGTA%2F6106These are warm in the way I like warmth... no detail loss. The tube plays less bass, but it sounds authentic and good to me...solid, fresh, deep. They have very good balance, sweet midrange without affect...just sounds real... really good textures (harmonics and micro details).
The 60 RCA 5Y3GT, by comparison, still has a very nice midrange with good texture, but is a little less balanced in my system having a sloppier bass, less micro detail, and less high extension. They may be good with your speakers though, the bass and "warmth" different, but more similar to my Winged Cs...could be the Bendix are a little too clean for you....I can't say, but what a well made and even sounding tube, doing all the stuff it does exceptionally.
The Valve Art 274B are well balanced, open, really good texture, big in a very spacious way, and more push than any of the above but without being in your face. The excellent ambient information and spaciousness, with a slight warmth, and great texture, brings pleasantly rich to mind for me. I find them very detailed but not harsh. Compared to my Russian tubes, they may be too bright in your system. They sound great here.
Hope this ramble helps. This is not easy. And remember, my system/room does tend to bass, and though I have tuned it out for the most part, I have kept it close to the edge liking deep but authentic, tightish bass.