Great deal for a great unit! GLWS

If I needed a one box for everything type of device this would probably be it

What's the difference between the signature and the regular iFi Pro iDSD 4.4mm — besides the much improved power supply?

As noted, the power supply and I believe they use an upgraded digital chip.

I actually had the IDSD Pro on loan before switching to Signature and can confirm that for my set up, the background is darker and dynamics were improved, especially in the bass. [These benefits tend to occur with improved power supply in general]. I also felt a bit more warmth in the midrange which helped musicality further. It's why I kept the Signature despite the premium at the time.

And of course, the below taken from iFi's page:

The Signature takes the original Pro iDSD and pushes it even further towards perfection.
The Pro iDSD Signature has:

• upgraded power -supply components to lower the overall system noise by 300%
• precisely matched NOS GE5670s tubes
• added support for USB1.0 (PS4/PS5)
• a new aluminium remote control
• a top-of the range iPower Elite power supply included

Thanks for the clarification!