Tube Adaptors For Havana

Curious; has anyone ever tried a tube adaptor with the Havana, like a 6CG7 TO a 5670 base. I have some Audio Research stuff that runs the 6CG7's and wondering how they would sound? Also wondering about the Toslink US 144 (usb to spdif converter recomended by Steve N.) anybody tried this converter with the Havana, just wondering how much improvement?
Make sure they can be changed in your amp before trying the
switch. The specs are different.I hope somebody could give you
the answer you need.