If a 600 is the desire.... then wait for it.
bi amping gets a lot of pub here. I've asked similar questions. From the responses I came away thinking of things this way.... Simpler is better.... and cheaper.
buy back to back serial number amps and I've heard from more than one designer, they're not going to be exat in all respects. meaning the likely need for attenuators as well as duplicate wires, stands, spkr cables, pc's, etc.
hearing the Big Mac, Krell, & BAT amps, if the Pass is akin to the levels of it's competition, and a big Pass was my sincere thoughtful desire, I'd make do with whatever and wait. Avoiding the turnstile & loading dock affairs with buying selling and shipping 2 - 3 amps, vs just one or two.
But that's just me. I'd bi amp the 802D's with tubes on top instead. or just use Levinson or the like SS amps. TBT, I like the MC 602 a lot and they keep pretty stable resale prices too.
have fun though with whatever.