12AX7 vs. 5751

I'm getting my first tube pre (Counterpoint 7.1) this week or early next week, and of course I have start fiddling with it ;-) I've been reading Joe's Tube Lore (http://www.audioasylum.com/audio/faq/joes-tubes.html) and the 5751 caught my eye, however I see statements like "lower gain that the 12AX7" and lower "mu" (what is mu?). Anyways could I use the 5751 tubes in my Counterpoint without causing any damage? altavistaaudio.com mentions nothing about the 5751.

thanks