Father in law gave me a nice vintage turntable so I ordered the Sonos Amp and received it with much excitement. B&W speakers are on the way but for now I don't have passive speakers which made trouble-shooting interesting... 

TT and phono stage to line-in on the Amp streaming to my Arc and one SLs in the other room and... uuuggh... a quiet, harsh, tinny sound with ZERO bass.

So... after hours of fooling around I'm still at square one. In a nutshell this is what I've done:

-Tested the turntable (phono stage has a separate headphone jack... sounds great)

-Used other line-in sources to the Amp... my phone, cd player... all sound great.

-I even hooked up an audio interface to the turntable and then to my Amp. It has a line-out so I was sure I was getting a line level signal. This also sounded great. There's obviously some ADC going on in there and this solved the issue... not sure how?

As soon as I put the exact same same line-out from the phono stage back into my Amp directly I get the quiet tinny sound again. Any ideas of what i might have missed?