I can't help you with the Mac or getting it talking with the PS3 but you may find it easier to get the Mac and a Western Digital TV
Live (~$85) working. The
WDTV Live plays almost anything effortlessly
but I don't know about itunes music and it will not play the lossless sound tracks from a Blu-Ray rip. DTS 5.1 yes but not DTS-HD. As some members have discovered the hard way DTS-HD is a PIA to get working with anything but a purpose built home theater PC and that's still a PIA to get working.
Only you can decide how screen size effects your vision issues so I'd get to the store and look for yourself. If bigger works for you then you have your answer.
Looking at your drawing I'd start by getting the L&R front speakers out of the corners. You always want at least 18-24 or more inches between the front speakers and side walls and you want the tweeters to be at ear level. In a 5.1 system the surrounds go directly to your left and right and a little higher than the L&R fronts. The room is so small (< 800cuft?) that a little 10" subwoofer like an
Outlaw LFM-1 Compact ($339 shipped) should pressurize the heck out of that room with the doors and windows closed. You'll have to
experiment to find the place that it sounds best. I'm sure someone else will be along with other suggestions as well.
For the rest it's hard to say without knowing how much budget you'll have left after the TV. Perhaps last years
Denon AVR-1911 receiver ($400 shipped). It's a good little receiver with all of the features you're likely to need and has plenty of power for a room that size.
Assuming a $500 speaker budget then a pair of
Infinity Primus P163, the PC251 center, and a pair a P153 for surrounds would be a nice choice. The P163 and P153 are front ported which makes placement easy. If the budget is $750ish (w/shipping) I'd consider Ascend Acoustics'
CBM-170SE bookshelves and center and their HTM-200SE as surrounds. The 170s are rear ported and need a good 12-18" behind them for the port to work but the HTM-200s are sealed and can be wall mounted.
Let us know f you have more questions and how it turns out.