which preamp for my cary slam-100 mono's?

CAry SLP98 F1, another vote.

I used to have Slam 100s with a regular SLP 98P. It had a lot of drive. Based on what I have read, I would be apprehensive about going with a SLP 98 that is direct coupled...there would probably be a loss of some of that tube magic.
IMHO, that combination had a lot of slam...it is 95 watts in triode. After all, that is the name of the amps.

Also, the Slam 100s did very well with JJ KT88 blue tubes. The music was more refined. If you do end up with a SLP 98, RCA 6sn7 grey glass work very well in the front sockets of the pre.

Enjoy building your system.

I ran a Klyne 6lx3p pre amp with mine when I owned that amp driving a pair of dunlavy sc III's;what speakers are you going to be driving?

I used to have SLM-100 with Cary SLP-98..

CARY SLP-98...VERY MUSICAL .

I did tweaked with a 6ns7 tubes and found out

1 pr. sylvania gtb in the back.
1 pr. of russian 6N8S ( metal base w/ 1578 stamp)in the front...ooooohhh...it's heaven!!!