Why do you think that borax would cause problems?

Revolution is very effective for fleas, but it has a relatively slow kill time (takes about 4 days for fleas to die). Flea life cycle stages in carpet may take a while to be killed, too, as they have to hatch and eventually get onto your cat. Could take a month or so to completely rid your house of a severe infestation problem using a topical like that, but it will work.

Not sure what your reservations are about borax, either, but if you are patient, it won't be necessary. Capstar will instantly kill all fleas on your cat(s) but effect is only 24 hours, and fleas that have not gotten onto your cat by that time will still survive (though Revolution will get all them eventually). Program is probably totally unecessary and not that helpful in your situation.

I would use the DE and it's safe for aniamls to walk on.

Forgot to mention, make sure it's a food grade DE.