There's a 16 page thread on this very subject on Talk Bass. Lots of opinions, some quite intelligent and informative:
[url="http://www.talkbass.com/forum/f15/genz-benz-streamliner-tube-rolling-796088/"]http://www.talkbass....rolling-796088/[/url]
I've re-tubed my own Streamliner with a NOS Jan Phillips 5751 in the V1 position and found that it noticeably tightened up the bass response without significantly reducing volume. A 12AT7/ECC81 has even less gain (60mu) than a 5751 (70mu) and a 12AU7/ECC82 (19mu) is pretty useless in a MI preamp and is best saved for home hi-fi aficionados.
I also replaced the V2 & V3 with some old RCA 7025's (those are military spec 12AX7/ECC83's) which are subtly warmer and quieter, but in a loud band situation are indistinguishable from the stock tubes/valves.
I also push it all into a Barefaced Compact (soon to be joined by a Midget). Mercy, mercy me, it does sound so very good. Warm, deep, huge and punchy tone no matter how loud you go and stays that way up until the police arrive.