Thanks Alvin, glad you are enjoying your Modwright 999ES.
Maril,
I don't have experience with Modwright's 3910, but I have owned he 999ES and now have the 9000ES. Assuming that the power supply and tube stage is the same, then I would think that the results would be the same.
Tubes are very subjective to your ears and your system. In my system, on the 9000ES I have great success with GE JAN 7044s. Another tube that works very well is the Philips SQ E182CC, a little more detailed and extended than the 7044, but not quite the midrange of the 7044. Either way, both of these run circles around the T-Sols in my system.
The umbilical of choice is made from cryo'ed Jena Labs stranded copper wire, terminated with Neutrik connectors. It makes for a more dimensional soundstage, and adss an analog-like naturalness to the midrange and extremes that the silver does not do, at half the cost. In a word, it adds "musicality" to the player.