I have used the 140 with stock tubes and have had no complaints. The real trick to making this amp sing is a very good front end. I have retubed other amps using NOS and it can get costly and frustrating. I think the idea of attacking the 6922s is a realitic start. Amprex will more than likely be the way to go. Siemen CCAs will be fast, clean (quiet), accurate and musical, but a little thin in the upper midrange. They also get you close to the performers being in your room. The Telefunkens place them in the room behind the speakers (not to be confused with a deep soundstage, but rather recessed). Telefenkens will also be drier, albeit fast and quiet with a small soundstage. The Amprex will give you all that the CCA does, but add some body and warmth to the midrange without making it bloated. But these are what my ears have told me.
Regardless, try the amp as is first. If you are going to tube roll look at the cost and see if you can use that money eleswhere in your system first. The 140 is a keeper out of the box.