DAC suggestion to pair with MC275 & Usher Spk

Certainly 2 MC275 are a good solution. However, think about the heat and the expense of buying/rolling/replacing that many tubes. Might not be an issue for you.

With 2 identical amps you could:
1. Operate each as monoblock and have them reproduce the full bandwidth to each speaker.
2. Have both amps operate as 2-channels, and have amp A feed mids/trebble from channel 1 and bass from channel 2. Same for other amp. Dividing the frequencies prior to the amps would still need to be dealt with.
3. Have both amps operate as 2-channel, but now have amp A drive hi/mids of left and right speakers and amp B drive bass on both speakers.

Keeep in mind the 501 are monoblocks, so they couldn't drive both speakers.

I'm personally inclined for tubes for hi/mids and SS for bass, provided a crosssover sits in front of them. Maybe a 501 is too much (power and expense). Maybe a 252 would do - depends on your speakers and budget, of course. This would be like my option 3, but with SS for bass. I don't know what advantage is there to have with ttubes for bass.

Certainly the speakers you have aren't easily 'digestable' by tube amp, but integrating them with sub can give you a possibility to keep tubes. If you aiming for more control, than certainly getting MC252 or MC352 will justify your goals(if we speak in terms of Mac)
Financially and logically adding 2x2Wq is a lot cheaper. Having MC275 is more like investment that will never lose the value just like gold so I would think forever before I would decide to sell this unit.

I have been greatly enjoying my system, which includes a tubed DAC. I run a late 2009 Mac Mini to a Lenehan Audio PDX Level 2 DAC to an MC 275 MKV out to Totem Acoustic Forest speakers. I have swapped out all of the stock tubes on the MC275 (12ax7s = late 1950s Bugle Boys, 12at7s = early 1960s military spec Mazdas and KT88 = Shuguang Treasure Tubes). I have not yet upgraded the tubes in the DAC (currently Gold Lion 6DJ8s), but understand that dropping in Amperex 7308s will make yet another big difference. The detail is tremendous, with female vocals and acoustic instruments, in particular, really shining. Very, very involving and emotional system. I'd strongly recommend trying out the PDX if you can find a way to do so. Good luck!

Rbw,

I understand Lenehan is a boutique shop out of Australia, with very limited distribution. Do you know if they distribute elsewhere? There was a forum member whose userid escapes me now, who has a PDX and kept speaking highly of it, but also mentioned the PDX was more like a work in progress than a finished product, so being close to the manufacturer was a big benefit (he was down the road from Lenehan).

BTW, I wasn't aware the PDX was meant to directly drive an amp.

It's true that Mike Lenehan has very limited (no?) distribution in the States. He has told me that his preference is to engage directly with audiophiles and rely on word of mouth rather than sink money into marketing. I have very much enjoyed the conversations on the phone and via email that I've had with Mike. He is very, very accessible and completely committed to helping you get the most out of his DAC.

If you happen to be in the Bay Area, I would be more than happy to work out a listening session.

Mike has designed the PDX to be an upgradeable platform, so in that sense, yes, it is a work in progress. I found this to be a plus, but perhaps others won't see it that way.

The PDX can drive an amp directly; that was a key requirement for me. The analog volume control is optional, so buyer's choice on whether or not you'd like to employ it as a pre-amp. I'm using unbalanced Harmonic Technology Pro Silway MKIIs, at the moment. I've tried Mike's RibbonTek interconnects, but could not discern a difference between them and the Pro Silways.

Let me know if you have any other questions!