my suggestion would be to get (or copy) a prooved audio system, eg. http://www.xi-machines.com/xi_de/xi_systeme_audio_de.html
latency / voices / CPU / instruments ( i can't find the figures @ 128, but you get the picture)
core2quad Q9650: 256 / 450 / 96% / 13 - 512 / 670 / 98% / 18 - 1024 / 800 /96% / 23
single core i7 950: 256 / 890 / 65% / 27 - 512 / 1140 / 66% / 32 - 1024 / 1250 / 63% / 36
dual XEON 5550: 256 / 1000 / 63% / 30 - 512 / 1300 / 63% / 36 - 1024 / >1500 / 60% / 40
hth, christian
and remember: only a CRAY can run an endless loop in just three seconds.