I've not had any heat problems with the Burson V5 Duals in the "topless" PB2. The only problem I've had after getting two that were not defective on arrival is that they were too tall to close the lid. :-) I still love their sound, but so far, I like the Sparkos SS3602 a little more.
The V5i should be a much better fit for the PB2 than either the V5 or the Sparkos op-amps, so I might try those eventually.
For only $55 U.S., you've really got me...