My recommendation would be for the 6SN7 based preamp the Cary Audio SLP-98L. Beautiful unit with remote power supply chassis and an uncanny realistic tone quality but I fear the gain would be too much for the Chord amp and the Rothwell attenuators did not work well for me.
The Rogue Audio units are fantastic but I recommend to stay mid-range and go with the RP-5. I had the RP-7 and it was too burnished and polite sounding and did not respond well to any NOS tubes. The RP-5 sounds smooth and still retains excellent detail. Nice looking unit too.