better sound from sonos connect

Just went from a bose bluetooth receiver to a sonos connect for my outdoor speaker setup (4 niles rs8si around my pool driven by a niles si-2150 amp, 2 def tech aw6500's on the house straight off my old yamaha rx-v671, and 2 niles gss10 in ground subs on a niles swa-500)  Currently I have the def techs running off of the head unit, and have been lined out into the niles amps with a volume knob at the pool 100 ft from the house.  Wiring is all 12 to 2 months old (recently went from 2 straight from the yamaha, to adding the amp and remote volume attenuator and going with 4 speakers, because more is better.)

The def techs seem to sound fine running rca's out of the connect.
The 4 niles rock speakers sound like crap, muddy bass, just absolutely sloppy, I thought I blew them until I tried running RCA's straight off a tablet into the amp and everything cleaned back up, I had better results with regular FM radio as well.

For some reason I've tried running optical into the yamaha receiver, which runs the def techs fine, but I can't get it to pass the audio out.  Reading up on the receiver, it seems it doesn't pass through the digital to analog.

My thoughts are do I need a stand alone DAC to get a cleaner signal since the anaolg signal pretty much sucks from the sonos? The logitech and bose bluetooth receivers I ran previously were much cleaner and tighter running rca out.

Obviously we're talking outdoor speakers, I don't need ridiculous quality given its the hardest environment to make function well, but the pool speakers honestly sound like crap and its driving me nuts.
I use a Wyred4Sound Remedy into a DAC (W4S DAC2) and it sounds great... this is is from a Sonos Connect as source. Relaxed sound w/ decent imaging. Upgrading the DAC is the next step.