@smodtactical
You've made a significant investment with that ARC preamp. Stereophile called it a reference piece of gear and that's not something they do lightly. Since you have the 6550 tung sol tubes coming, you should definitely see what kind of difference that makes. But chances are with that preamp, I'd expect there to not be big changes.
I think you'd get more enjoyment out of building a preamp than you can imagine. You become much more involved in what you're doing. The SP14 uses 6SN7 tubes and there are many different brands of 6SN7, so you'd definitely have more to choose from. The cost of the SP14 kit is low enough relative to what you've obviously spent elsewhere in your system that you can afford to experiment.
It's a little like comparing the experience of buying a new, hi-end Porsche versus an older sports car that you do all of the work on during weekends. The new Porsche is an exceptional machine. Too perfect perhaps. But that 50 year old Triumph begs for you to know every inch of it before you even get in.
If you really want to get your hands "dirty", consider building an Aikido circuit preamp with one of the boards from Glassware Audio. It's the same circuit that the SP14 uses, but you'd be using a different power supply and you'd be building it all from scratch. Then you get a lot more choices regarding power supply, caps, stepped attenuators, etc. Now THAT would be fun!
