Question

I want to connect an external pre-amp to my 68c which as pre-amps on it's 4 inputs. is it possible to by-pass these and just use the 68c AD converters for the external pre-amp?

Answer 1

The 68c manual implies that the pre-amps are only active when using the XLR mic inputs and that using the 1/4” line or instruments inputs are not routed through the pre-amps.  Unfortunately, there is no block diagram in the manual to verify this.  To verify you should email Presonus support directly.