First off, I own a Bifrost and Lyr, great products, thank you so much - I look forward to blowing my Christmas bonus on a Ragnarok/Yggdrasil.   You mentioned muting volume between steps on the Ragnarok volume control - this is a great consideration!   The Burson HA-160D amp/dac exhibits this...

I have coaxial, optical, and USB hooked up to my Bifrost Uber / Lyr stack and switching between the three input types has no noticeable difference to my ears through LCD-2 and HE-500. 

  Thanks for the info!   Switching between the three, I don't hear any sound quality difference with HE-500s. I listen to FLAC mostly. I'll switch to USB and leave it alone.

Great thread. I look forward to these posts every week. One question, however:   I own a Bifrost (uber/usb 2) and Lyr, attached to my (modern stand-alone) PC sound card.   My PC supports optical, coaxial, and USB.   Is there any reason to use one over another when all three are available...

  I wouldn't bother with the upgrade, to be frank. Save your money. Even in the likelihood you do hear a 5% improvement in sound quality, is it worth the 400% cost difference? Unlikely. It's easy to get caught up in the never-ending chase for your "end game" sound. Wait until you have enough...

I think the Lyr sounds great with r2.2

  Thanks for the info!

  Pardon my ignorance but what exactly is the goal of 'summit-fi' and how does it differ from what's being offered up in this thread? Is summit-fi just a bragging rights thing, or is it actually a different philosophy? Thanks in advance.

I'm interested in upgrading from the Lyr, can you elaborate on what you mean by this? My other pair is HE-500, thanks!

I couldn't hear anything significant either.

  The money might be better spent making that PC silent. Antec TrueQuiet case fans, SSD hard drive, fan controller unit for the GPU - water cooling system. In order to fully appreciate any increase in sound quality from audio gear when using open headphones, you want your noise floor to be as...

  I don't believe there's anything wrong with USB 1.1 - a 24 bit 192khz audio stream is only 9 megabits per second. USB 1.1 tops out at 12 megabits per second, so you shouldn't experience any issues.

No. Only if you listen to 24/176 content.

Yes, positively.

  Same here - Bifrost Uber / USB Gen2 fed from a Win 7 PC   Creative Labs Soundblaster Audigy 2 ZS for the toslink / coax passthrough and mobo USB header for the rest