Well as I said I can't speak for the 2nd set up, but relative to what I do have, IMO the soundstage of the MPX3 that I have paired with the Lavry is superior to the Lavry out of my transport. There is greater warmth and clarity as opposed to the Lavry's headamp. That being said I do not feel its necessarily a comparison that one should make, you have a sound that is decidedly solid stae vs. a tube amp. That said I do think that they work well together and the fact that you can tube roll (change the presentation) is always a plus.
That being said I feel that there is no comparison, if I had to keep one only I'd go for the MPX3 (or PPX3 SLAM or with proper upgrades)
The tubes that I use are the mainly 12sn7GT, 14n7, 6BL7GT and 6BX7GT. Those are octal tubes that do not require a tube adapter with the exception of the 14n7 which is a loctal tube. If you're looking for tubes for the 701s or Grados, powerful output tubes like the 6BL7GT, 6BX7GT, 5687, 6350, 6463 are favorable compared to the 6/12sn7 as they can provide the necessarily current to drive the lower impedence cans. realize that if you wanted to use 5687s, 6463 or 6350s, you would need to buy tube adapters from Mikhail as well.
But yes tube rolling is fun and useful as I can tailor the sound to what I want it to be as oppoised to being fixed with one type of sound. That being said for what it is the Lavry's headamp is no slouch and for what you get I also think it's a great bargain, also consider the fact that Lavry's customer service is second to none. SP's service is great as well.