Best sounding tube for Audible Illusions M3A preamp?

I am interest in learning what folks are using as the best tube for preamps, specifically, the Audible Illusions Modulus 3A. (My AI M3A also has a Gold phono stage card, but that is purely solid state). I have reviewed nearly all the tube roller-specific forum threads here, which are spread over  several topic areas. I have also reviewed another thread located elsewhere (https://www.head-fi.org/threads/6922-tube-review-17-top-6922-6n23p-e88cc-cca-7308-e188cc-tubes.76107...). I know that AI recommends the 6H23n tube for the M3A. So please let me know your thoughts about this tube and whether you can recommend a particular brand of the tube and commercial online supplier. I would also appreciate your view of alternative tubes (including brands and online suppliers), should you recommend something other than a 6H23n tube for the AI M3A.