Nuforce 9 SEV2 mated to Transporter - what pre?

I had my Nuforces for about 5 months now. I am thrilled at how these amps simply lack any sonic signature I can detect. Whatever I put around them simply seems gets amplified. Sorry I can't descibe what I'm hearing properly. Dead silence then music, all of it. But something is still missing.

I'd been using a SB3 that I modded and now own a Transporter. After a considerable amount of critical listening I have come to the conclusion that as clean and dynamic this combo sounds, it lacks soul. I knew beforehand that the omission of tubes in this setup would have to be addressed. My plan was to send the TP to Modwright and add the tube output stage. Now I've decided that before the TP gets modded, if it does at all, I want a tube preamp. My current setup is no preamp at all. I have some idea's from posts that I've read.

Dodd battery
Audio Horizon 2.1
Modwright 36.5
other???

Thanks for your advice!