[junkgear]

Some would argue that S/PDIF is your best option since there is less conversion from analog to digital. You did not mention if your interface supports this though.

If not, then you are correct that the Amp outs are not balanced and are also instrument level. These days audio interfaces can handle a wide variety of signals, so before investing in a DI box, I would give it a try and see if it is acceptable for your use.

If not, a DI box will provide a balanced out plus some isolation. In this case, you would run the amp out to the DI box, then the DI box into your XLR input on your interface.