I owned the Cary SLP-98P for a couple of years a while ago. While I never did a direct comparison with the Rogue 99, I have heard from others who are familiar with both that the Cary 98 is quite a bit better.
As for tubes, I am familiar with the Sylvania VT231 (6SN7 equiv) and the RCA Black Base 6SN7's. Sylvania NOS VT231s are not cheap anymore and, by far, the better of the two. If Sovtek 6SN7's are like any of their other tubes, they are not any where close to a good set of Sylvania VT231/6SN7's.
I know someone who has a Rogue Perseus pre' and is considering a Rogue 99 or a Cary SLP-98. If he gets both pre's in for an audition, I will ask to have a listen and report back.
Not sure if I can address the "more focused vocal image" you mentioned, in connection with the pre-amps or the tubes. Syl VT231s have lots of physical heft (in their sound), in general, though.