never tried the channel route, always done the desat way and adjusted slightly the contrast with curves
when going for a white BG be careful that the BG isnt too dark..you end up changing the whole image whilst getting the white..better way to do it would be to use dodge tool, set it highlights and i use 4%. slow rub over BG getting desired white without changing anything else..

__________________
The summer is here and the time is right,
We're going racing in the street..

Canon Forever

1Dmk2,10D, 20mm,28-70mm,200mm, Elinchrom3000,1500,600's,500's, Multiblitz200,Bronica SQb, expensive Manfrotto tripod