the post from 2008 regarding sound quality was before vicibox came out from The Vicidial Group. At the time, we were using Gentoo with good sound quality. Now we use Ubuntu (Vicibox) or OpenSUSE (Vicibox Redux) or VicidialNOW (CentOS) or Scratch install on Gentoo. All give good quality calls (Ubuntus problems were resolved last year by The Vicidial Group).
I have not yet noticed a sound quality difference between 64 bit / 32 bit OS (but admittedly do not get a lot of requests for 64 bit, so we do not test that a lot). We also have not found an improvement in quality by adding the word "Xeon" beyond the fact that you can multiply the processors and get "More CPU". So our Core2Quad and our Quad Xeon testing has so far shown no noticeable difference between processors IF all other items are the same (L2 Cache, Front Side Bus, CPU Speed, # of processors). But (unlike Core2Quads!) you CAN put multiple Xeon's in a properly outfitted motherboard and end up with 8 or more CPUs. Now THAT is nice.