I looked up the Lad2 pre-amp. It uses two 6SN7 tubes so you are in luck as far as tube upgrades go because you can still buy beautiful examples of NOS or just OS (Old Stock = used) Tubes. The only way to know which tube you will ultimately like, is to try some. IN general the more expensive an NOS tubes is... the greater is the demand for good reasons. To save you time but not $ try Sylvania "W"s or GTs for an all around great sounding and stage throwing 6SN7. If you like anything specifically such as bass (iness) let me know and I can give you some suggestions.
I don't know about the capacitors.
I don't know about the capacitors.