Not even a warehouse chain as dedicated to best buys as this one can compete with the prices of low-overhead electronics retailers in the virtual world. So what Best Buy has offered increasingly in recent years--particularly through its cavernous store off 494 near 35W--is breadth of product and convenience of purchase. Most likely the prole knob-twiddler will want to conduct some of the bigger transactions--for a new home-theater amp, say--online. But where besides Best Buy can the impulsive, obsessive electronics nut duck in on a moment's notice and grab an armload of Monster Cable, a stack each of CD-Rs and DVD-Rs, a laser-printer cartridge, a PS2 disc, a pack of AA batteries, and a dustbuster?