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Cairo is claimed to improve gtk's already fairly slow speed. And unless you actually try and take advantage of it with your theme I doubt you'll notice a speed difference. In fact, the favourite gtk theme today is probably clearlooks, which shines in speed more than it does looks: I found it to be noticeably more responsive than default (I had to use a 350 PII on Debian to figure this out). Anyway, eye candy has usually been KDE's thing.
I've never seen an app I couldn't get installed on a recent (less than 2 years out of date) system. Commercial apps doubly so; they're usually statically linked and you just run an install.sh and give it a directory. Then read the explicit instructions on updating LD_LIBRARY_PATH and PATH.
I doubt there's good professional audio card support for very many audio cards. If you're a professional audio guy you should probably go with the OS that the few professional audio hardware and software makers recommend: OS X or XP. Linux is for everyone; Linux driver and software support isn't. We don't call Windows crap because it's hard to get our make, gcc, latex, sh environment going do we? Well, I probably have, but that's usually just a shout of anger at cygwin .
Alsa is the standard linux sound driver system. OSS is the old standard linux sound driver system; very very few distributions default on it. ESD is a sound server because OSS was lacking audio mixing. ARTS is a sound server because OSS was lacking audio mixing. Jack is a software library for most audio applications.

Sorry to get off track, but there's an awful lot of anti-linux posting in this totally unrelated thread.

Also, if you got Archlinux going and you can't install rosegarden... Well, something doesn't match up. Arch makes Slackware's hardware detection look good. The first time I installed it, I had to turn sound on (it was somehow off in devfs as I remember)!