you'll never go wrong with rogue's. they're the best bang for your money. the preamp pretty matches with its own kind. you will definitely love the transparency and the tightness of the bass with 99 magnum.
have you tried using 6550 with your amps? i replaced my kt88's with 6550's and the detail is more appealing (with ultralinear mode). the kt88 is huge sounding but less on detail compared to 6550. anyway, good luck and enjoy listening!