An inexpensive good tube preamp (true balanced, use XLR)that worked wonders for me was the Cary SLP-2002. Use 6CG7 gain tubes instead of the 6922's to reduce the gain to match the high gain output of the X250. I used to run this combo & liked it better than a Pass X2 pre w/the X250. There are many past threads on this subject you can reference too.
