You might want to try your Kappalite 3015 in that cab. I recently picked up a pb100 combo and bx500 after seeing what you did with yours (thanks for the installation advice btw). I've been running numbers through win isd and the 3015 will give a much flatter response in a box this small than the stock driver. I don't have the specs for the carvin neo driver but the kappalite works well in a small box - it's not ideal but about as good as it gets. I may pick one up for mine. I have 3 gigs this weekend and want to see how mine does with the stock driver. I can hear the low mid bump already though just practicing in my apartment.
I would expect that low mid bump to be even more apparent with a 10" and that teeny box of the PB100. What kind of music is at the three upcoming gigs? Let us know how it performs.
The KappaLite 3015 is AFAIK only available 8ohm which cuts the BX-500 power to 300w, so I probably won't do that. And, the KappaLite nearly perfectly suits the R600 I drive it with.
I had never intended to run the BX-500 through the PB-200 stock driver which is a 200W 8ohm -- my philosophy is always for the speaker to have at least the power handling capability of the amp I'm hitting it with. Plenty of opinions to the contrary here and elsewhere, but it's my story and I'm sticking to it.