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You're probably best off expanding your search to include all of the NuBus-equipped Power Macs, as it will be easier to find a solution. An 8100 would be a little faster, and not any more expensive these days. A 6100 would be slower but I imagine it would still work OK. For what it's worth, there are a number of these machines on ebay now, including at least one 7100/80.
If the Audiomedia II NuBus card is fragged then you're in bigger touble, they are obviously less common than the PowerMacs themselves. You will then have to find an equivalent card...and PCI cards are much more common than NuBus cards. In that case you might consider getting something newer (like a G3 desktop/tower) since a G3 is probably not any more expensive than an earlier PPC machine and is easier to find parts for.
As an aside, many of these old Macs are cheap enough that it might make sense to buy two of them, so as to have a backup machine or a parts source. And while you're at it, it wouldn't hurt to shop for a decent UPS, that should prevent another lightning damage incident and can be used with any computer, so no upgrade worries.
Good luck!
