The best tubes for ARC LS16 MKII

Yes, the 16Mkll does indeed use the new 6h30 tubes. I am not aware of any replacements for these..maybe someone can correct me. The 6h30 is supposed to be a "faster"sounding more accurate valve. My listening impression of the 16Mkll confirm this as a good sounding and immediate sounding tube, but not as warm and transparent as my LS15 with NOS tungsrams.

Can someone clarify? Doesn't the Mk II use 6h30s? Are there NOS or other alternatives to the stock tubes AR provides?

Depends on your perference and there is no such thing as perfect.
I perfer Siemens tube over any other brand for Audio Research preamps. Hope this help

Check audioasylum tube FAQ