Yes - I think your making the right decision. The network / media server features of the Marantz AVRs / Pre-Pro's are not great, even using the Marantz iPhone app, which is also not so great. Better to use the Roku / etc for streaming media including music, which aside from having more services and better GUI's, is also wireless.
One thing the Marantz AVR's have which is actually quite useful is the "M-Dax" feature that really does make highly compressed audio, such as most streaming audio sources, sound considerably better. I found "low" or "medium" setting works quite well. Give it a try by pressing that button on the remote when you get it. Usually I'd use "Pure Direct" mode for regular 2 channel audio, but for highly compressed / low bit rate stuff, the M-Dax feature really is pretty good.
