I quickly looked at the manual for your pre and I doubt they are running that 12AX7 at 16V, but I may be wrong. Typically they are gonna run at a much higher voltage (100-250V) than that to optimize it's performance. You should stick with 12AX7's if that's what the manufacturer recommends. 12AU7's and their variants are gonna give you considerably less gain, plus the circuit could damage them or the whole pre if not set up to run them properly. A 12AX7 is a high gain tube. And since we don't have a schematic of the pre, it's really hard to recommend anything. FWIW, other 12AX7's may very well give your pre a different sonic flavor--and they are usually not all that expensive unless your going for Telefunkens or something.

My suggestion: call the manufacturer and discuss with them tube rolling in depth. Nobody like the designers to let you know what you can use and what you can't.