Tube Rolling A Pro-Ject Tube Box SE

Anyone try 5751 tubes in the tube box se? I asked the Pro-Ject rep and he said that they only spec 12ax7's and he never tried anything else.

5751s will work, but you'll get about a 30% reduction in output. Probably will depend on what cartridge you are running. I'd had some 5751s sound much better than their 12AX7 counterparts, but in different gear.