I would recommend to troubleshoot the Symphony II issues first. Before you start dealing with the RNS-E adapter issues.
If you have Bose all speakers are power by the amp in the rear, non-Bose A4 have the front speakers directly connected to the head unit. Try to track down where the problem might come from and fix those first.
If you have Bose all speakers are power by the amp in the rear, non-Bose A4 have the front speakers directly connected to the head unit. Try to track down where the problem might come from and fix those first.