Some time ago I had a similiar setup. Mac mini connected via HDMI (DVI - HDMI), composite, spdif, analog L-R and PUC (apple remote) to Beovision 7-40 MKIII, masterlinked to a BV6-22 and a BC6-26. For picture I used a HDMI splitter 1-4 (Gefen) and a HDMI-composite scaler (Gefen). For audio there was an optical-coax converter (Oehlbach) and a Philips surround headphone amp, which provided a digital loopthrough for the main system (PCM, DD5.1, DTS) and analog stereo for the linkrooms. Installation was a bit tricky, but after a while everything worked fine. I also installed a master/slave mains box, to disconnect converters, scalers, splitters, HDs... automatically from the mains, when the mini was in sleep mode.
Your setup uses a VGA-composite scaler, which means, the mac must be able to distribute DVI (digital) and VGA (analog) simultaneously. I doubt that it will work....(?)
For audio you will need analog stereo sound from the mini. The RF modulator can`t distribute digital audio. That`s why I used the headphone amp - provides digital (surround) and analog (stereo) sound simultaneously.
I switched from the mini to the Tvix 6500, because 1- the mac couldn`t handle HD movies (MKV) and 2- I hate the apple remote! The Tvix could handle nearly every video format and navigation via PUC was quite satisfying. Tvix also can send digital AND analog audio without any additional hardware. It was connected to my airport extreme via ethernet, where I connected my mac formatted hard discs. Now it was possible to watch an HD movie on the BV7 and/or in linkrooms, and watch ANOTHER HD movie simultaneously and wireless on a macbook / Mac mini using VLC.
Next step was to solve the Blu Ray problem. I didn`t want the Beo BD player, because it can`t handle HD audio formats (DTS HD master), has no network connection and is slow and expensive..... So I found an LG BD player, that can decode HD audio, can play HD movies via USB and network, is able to distribute digital and analog picture AND audio simultaneously, can be controlled via PUC and has a very fast start up - you can even use the BV7s electronic curtain - AND it`s quite cheap.
So I think, I have found "my" media solution for movies, for music I`m using a BS5. The Tvix is sold, Mac mini is now installed in my home office and used as what it really is: a computer (a really nice one!) but sorry, not a media server...
Hope this helps.
Stefan