I've used my HD800's with the Teac UD-503 and UD-501. My best advice is to use these Teac units as D/A's but not use the built-in headphone amp. The HD800's are driven OK by either unit's built-in headphone amp, but to be frank, the amps pale in comparison to many separate headphone amps...

Indeed, the Bryston and HD800 are a great combo. I've been enjoying this combination for several months now. It's probably my endgame amp/headphone combo.

I may be pretty late to comment on this, but you can't go wrong with the Bryston, especially if you like an accurate sound.

I've found that the HF5's benefit greatly by proper amplification (i.e., not using the cellphone output). I'm using an Oppo HA-2SE which does wonders for the bass. It's never bloated though, just right...

I have the HF5's which I like a lot. I'm using them with an Oppo HA-2SE d/a-amp. I do not find them lacking in bass response at all, but only with the amp (not with a cell phone driving them alone). Will I notice a vast difference if I upgrade to the ER4SR, or are HF5's just very similar?

Indeed, I'm very happy with both my UD-501 and the UD-503. I can't imagine that the UD-505 will be any different. Has anyone gone to the extent of connecting a GPS-disciplined 10 MHz clock to the UD-503? If so, any improvement?

The options are for either RCA, XLR2, or XLR3, so no way of driving both RCA and XLR2 (or XLR3) simultaneously. Has anyone gotten the UD-501 to work with Linux (I'm running Mint 17) at any sample rate other than 44.1kHz? Does it require changing settings in the OS?

I see nobody has responded to you. I have both a UD-501 and UD-503, one on my headphone system and the other on the "good" stereo system. I use the standby as a matter of course - just more convenient to power it on using the remote rather than the physical switch on the unit itself. It's all...