Help me deceide on pre-amp please

Guys
I'm looking for suggestions on my next upgrade. I'm leaning towards a new pre-amp. Perhaps a VTL 2.5 or maybe a Audio Research unit. I'd prefer to keep the price under $1500 USED.
A friend of mine was kind enough to let me try a Cal Aud Labs Sigma Dac on the O/P of my NAD and I did like the tube effect. It was not a huge improvement IMO but did add a certain bloom and impact on the upper bass and lower midrange. It was this audition that has convinced me to include tubes in my search but I am open to suggestions on both SS and Tubed units.
Ideally the preamp will have remote volume and HT pass as I plan to integrate this into a HT sys. I listen to mostly pop and rock music.

Here is my current 2CH sys.

NAD C542 CD Player
Aragon 8008ST Power Amplifier
Acurus RS-11 Pre-amplifier

Paradigm Reference Studio 100 V3 Loudspeakers
Paradigm Servo 15 V2 Subwoofer