Wally wrote:

What's the deal with choosing output powers when tri-amping?

Where's your crossover?
If you are still using the passive crossover from your speakers
then you will need the same power rating for all amps.

If you have an active crossover then the tweeter amp can be rather
lower powered. In theory you could get full power out of a CD at any
frequency but in practice the levels drop at higher frequencies.
An experiment on your favourite music with an audio editor such as
Goldwave will be helpful. Split it into three at your chosen
crossover frequencies and search for the maximum level in each file.
This will show the relative voltage and hence power required for each
amp, assuming all drivers have the same sensitivity.

Won't my T27s freak out if there's a 50W amp dedicated to them?

Only if it thumps on switch-on and you don't have the original
crossover.

Am I on a concievably-sensible track with this Cyrus Two idea?

Yes.

--
Eiron.