There's no dashboard, but at some stage during the 2x4HD thread, Amir estimates 90 for the HD's SINAD. Not a big step up I'll admit, but my experience to date is that 90ish with poor jitter rejection (eg Chromecast Audio) is around the point where I start to hear issues with the few DACs I've had.
Fooling myself? Could well be, but my guess is the Piano will be good enough. We'll see.
EDIT: Motu M4 looks great by the way, but in Australia, RPi+ Piano 2.1 is around $150 and the Motu is around $400. I'm sure it's well worth the extra, but I couldn't find one in stock anywhere anyway.
I think the Piano (and the 2XHD) are plenty good, obsessing over SINAD is often a rather useless exercise. Once you get it up and running I would take a look at running CamillaDSP on the RPi with just a pass through setup in PurePath. I've switched all of my miniDSP systems to RPis running CamillaDSP and have been super impressed. It is very easy to setup, super powerful, has a decent web interface and is very easy to integrate with other things (display, IR volume control).