Yes You can use other pickups with the Vari-mid preamp if You Like. You'll have to check the schematic if You want to run passive pickups go to http://www.ibanez.com/support/wiringdiagrams
and check Your blend pot value, the pups go to blend then to the preamp.
I had to swap out a 25k blend pot for a 250k in SR1015 that had their SFR passive pups (actually pretty decent).
I recommend a Bourns blend pot with MN taper if You need to go that route. If You're staying with active pups then just wire them in.
I'd still double check the schematic to Your setup. Good luck.