As per Burley's website, the chain and cassette on our Tosa were "SunRace," which was oh-so-not SRAM and lasted about 400-500 miles of fast riding with our 350# team before the shifting got sloppy. I replaced the cassette with a Shimano XT M-760 and the chain with a SRAM PC-991 and without a single adjustment to the derailleurs the shifting has improved 100%.
As far as the seatposts, I upgraded Mollie's to Rock Shox right out of the box, and I upgraded mine to a Wound Up carbon post to take some if the edge off the AL frame, which has worked great. I had no problems with my stock post for the month or so I used it...
Not sure how we got lucky with the White Industries hubs, though--Burley's catalog lists XT as the spec for the Tosa. We'll take it!
DrPete