There is no easy way to modify the V76 that works without compromising sound and specs.
I know several so called professional racks offer a simple DI input, that is more for marketing, it passes signal but not to studio specs.
Without going into technical details, in order to utilize the circuit for DI input, the entire front end needs to be changed, due to some minor problems of in-state feedback as RADD47 pointed out in a different post.
In the new V72 and V76 that features a DI jack, the inputstage gets switched, x-former, grid leak, feedback loop, etc. via a DPDT switch and an additional relay for the feedback loop. All signal (grid) wire runs are less than 2 inches...
In order to keep the amazing S/N ratio all wire runs need to be as short as possible, so you need to drill the face plate, otherwise you end up with approx. 12 inch of wire that sucks the high end and acts like an antenna loading down the signal with RF; you can not hear it directly but the sound gets mushy.
If you have a V76 or V72 with a burned out input, you can make a great designated DI box from it.....
Best regards,
Oliver