I would worry much more of your power amp than the preamp. I have a pair of JM Lab Spectral 913.1, it's a little lower model than yours. It's a hard to drive speaker. I tried a single ended tube power amp and it absolutely bombed. You need to try a solid state amp to compare.
Your VAC 200iq is a tube amp, damping factor is inherently lower, if you speakers is as difficult to drive as mine, you have to watch out tube amps cannot control the speakers. Also, for hard to drive speakers, speaker cable is very important as it will lower the damping factor even if you amp has high damping factor.
The preamp is the last thing I would concern. I don't even use preamp, I use a passive volume pot built into the power amp ( like integrated amp) and it gives me the best sound in comparison.
Own designed power amp, own designed preamp, JM LAB Spectral 913.1 speakers, Rythmik F12SE sub.
Not hooked up: Nakamichi Stasis PA-7 power amp, Velodyne VA1210 sub, Kef Reference Series center, Kef Bookshelf speaker, Monitor Audio bookshelf speaker, Infinity rear speakers. Acurus 3X200W amp.