Hi,
not sure how expensive rest of equipment is but unless files are recorded (I mean all instruments/vocals) in 192/24 I really do not see any point going over 96/24 for FLAC that all devices support.

To anser your question, yes MM4 and MM5 play 192/24 FLAC files.

I'm thinking about purchasing Hi Res flac ( 192/24) files on-line. I just want to know if MMW4 will play these types of files? Do I need any thing further ? I had a look through the knowledge base but couldn't find anything on this subject.

Furthermore, my old hi-fi preamp is connected to my network via a Yamaha WXC-50, the specs mention it supports FLAC / WAV / AIFF 192 kHz / 24-bit for high resolution reproduction, do I need to upgrade my pre-amp?