Hi Dom.
Firstly you probably know I am a mac man so my opinion is unreservedly biased! TBH I don't know if you have worked with macs before. I have owned macs since the end of the 80s when I had a wickle 512ke, with twin super drives (Super drive back then was the larger capacity floppy drive)
I have been using MAC OSX since March 2001, and what strikes you is you can count the amount of crashes on one hand, in my case I can remember 1 system wide crash or kernel panic in all that time, this will give you confidence in the work that you do. Plus I don't just surf I have created complex illustrator documents and very complicated 70 page plus word documents with many many graphs and graphics, not so much as a glitch from the mac. NO doubt many PC people will jump in here and say they have not had trouble but I think we can all stand up and be honest here, OSX is based on Unix and is in my experience 80-90% more stable than anything I use on PC and I use PCs a lot.
I notice there is yet another 'worm' for PC and Microsoft have rushed out with yet another Patch to try and block the leak.
You don't get this with mac.
Anyways enough of that stuff onto the question in hand.
The G5 has had one problem, the power supply started getting really noisy. By that I don't mean noise in the audio stream, just straight forward noise. This was replaced for me and since then it has been fine. The fans are very quiet, much quieter than my G4 which was not very noisy anyhow. Again not being funny but the G5 is quieter than most PCs I have heard especially considering what it is doing, 64 bit architecture must not be an easy load, and there are 9 fans in there! In terms of noise well I am sat right on it with a low volume TV episode of the terribly unfunny 'friends' unfortunately friends is beating the mac. You can't hear the mac on a silent day in the next room, but you know it has fans so you can hear it on a silent day in the room.
Onto the audio, well I have had a lot of time to digest the sound from the mac. As a recap its via itunes in general at 24000khzs AIff and a few files in the new apple lossless compression format. This exits via the optical out on the G5 into ten metres of cable, into the back of the arcam black box three then a short run to the 52/250/SBLs.
Sound wise, well its certainly compressed, there is no getting from this fact the compression screams at you. Primarily what is missing is detail and mid range. I liken it to this. The mac (or compression) seems to offer the bass depth and treble extremes you get from a decant CDPlayer, but its missing the bit between the deep bass and mid range and the bit between the treble and the midrange. What you get as a result is initially a very impressive sound, but it becomes fatiguing, and sometimes down right annoying. I don't believe this is an inherent problem with the mac. My reasoning is that in the optical out mode on the mac, the internal preamp is by passed, volume control does not effect the output, i.e. the mac has effectively become another source component.
I believe some of the problem will ultimately come down tot he arcam, I don't rate arcam I think in fact it is second rate pap which could reasonably get away with being sold in Currys or Dixons, and it certainly is not a patch on the Dac64 I heard when Merlin came over. These facts for me must be accepted, so too will the fact that the CD has been halved in size and placed onto a harddrive which has to then be sourced and played out of a computer which is doing other things.
One thing I can tell you is that it dosn't matter what you do you can't get itunes to skip, this is important, I do a lot of stuff on the mac and I don't want every mouse click to result in some sort of f**up on the audio out. the mac has true multi tasking and it simply does not skip. I use the CDPlayer on the PC at work and you can't even open Word without the thing skipping and blacking out.
Currently my conlusion to all of this is:
The Mac G5 pisses on anything I have seen in the PC market and Mac market, this is not just a biased opinion, it just screams quality at you., This thing is made from solid aluminium, it starts up in 14 seconds (yes I timed it) and one day for a larf I clicked all the application buttons in my dock at once (42 apps) they all loaded within 40 seconds, no crashes no problems.
The sound out is very good for what it is. I might just be spoiled with what I have become used to, but aside from the negative comments above, the sound is genuinely impressive, there is a lot of forward projection into the room, far more with Naim CDPs and stero separation is excellent, bear in mind the optical out is ready for 5.1 as well
What ever you go with, check out the application itunes catalog, it will do this to your music library:
And you can also access your music via you browser in page order like so:
What ever you do buy loads of memory and have fun!