I have an Audio Note L3 kit pre-amp that has the same tube compliment and similar circuit as the M3. Tung-Sol 5687 tubes can be recommended along with a Mullard 6BM8. Some RCA and GE 6BM8 tubes are re-branded Mullards which can be verified if they are labeled Made in Great Britain. The Telefunken ECL82 is a good 6BM8 type, but a bit leaner than the Mullard. I also like the Bendix 5852 tube as a replacement for the 6X5GT.
Hope this helps.
Hope this helps.