Hi Bob: I haven't heard the battery 900v vs. the 8001. Although I can tell you that the TRL 8001 is the best I have heard to date. Also I beleive you may see some 900v battery's for sale in the near future. A lot of detail with tremendous solid bass and the warmth of the tube sound. It's all in all for sure.
Best regards and have a great holiday season !
Best regards and have a great holiday season !