The 912 is an excellent do-all pre/phonos; one of the very best and is on my list as my next (retirement) pre. I have been told that you can 'warm-up' the overall tone of the 912 with some choice tubes.
Two possible contacts that may be willing to recommend alternatives:
(1). Kevin Deal at UpScale Audio sells a lot of tubes destined for the 912
(2). Bob Levi, president of the Los Angeles Audio Club is a big fan of the 912 and has used it extensively and would probably give some recommendations if asked
http://www.laocaudiosociety.com/index.html
Two possible contacts that may be willing to recommend alternatives:
(1). Kevin Deal at UpScale Audio sells a lot of tubes destined for the 912
(2). Bob Levi, president of the Los Angeles Audio Club is a big fan of the 912 and has used it extensively and would probably give some recommendations if asked
http://www.laocaudiosociety.com/index.html