The system that came in our Legacy was garbage, too. Did like you and got the RV760 - love it! Only use the in-dash system for the cameras. For sound, we got a wireless Bose speaker and set it up in its cradle on the kitchen counter (plugged in and won't move around), then connected with our iPod. Fantastic sound! SO much better than those two 3" speakers the FR folks decided to mount on the ceiling, hidden behind the electric bunk!
2015 Legacy SR340 360RB
2014 Jeep Wrangler Unlimited Toad
Gigi, Poppy and Sadie Lady...On the road, but not full time!