Is there a killer preamp for 1500?

Yes, I think you should expect a similar sound. I've always thought Cary's weakness was on the low end, but that is not to say their tube gear doesn't exhibit good bass. I think it's typical of the Cary house sound to be a little bloated on the bottom end. Mids are Cary's strong suit IMO.

The direct coupled mod evens out the sound, tightening up the bass, and providing some additional speed. Maybe an SLP-98 with this mod would be appealing.

I've been having a bit of bass bloat lately due to slap echo and some properly positioned acoustic panels solved that problem.

They are different animals but you'd be surprised how similar they sound. Cary seems to do a great job maintaining their house sound and both are evident in the SLP-94 and 98. IMO the SLP-98 gives you more flexibility to tailor the sound with 6SN7 tubes and their variants, as well as bit more extension. Of course if you go the F1 or direct coupled route with the SLP-98 you would be deviating from the original design path and sound.

Bear in mind that Dennis Had got a lot of mileage out of his SLP-50 design (even using it as the basis to design the NEW P-3 which was an private labeled Cary product I used to own). Also, consider the AES preamp that uses 6SN7 tubes is sort of a cross between the SLP-50 and SLP-98. In a sense all of the Cary tube preamps, with the possible exception of the SLP-05, share some lineage.