I used a D.I. box because that is normally how I connect things and I used the best D.I. box I have the Radial Pro. If I use the TRS input jack instead of XLR on the MOTU 896Mk3 Hybrid then it bypasses the preamp in the unit. A low level "instrument level" isn't enough. I had the level control on the CabDryVr at max so it would equal the input signal level from the guitar. The MOTU 896Mk3 Hybrid does not have a high impedance "instrument" input like some other units.
In the bypass mode, the unit did not cut the highs, but when used it did. The "Size" control didn't do much.
Why would I want to try and EQ the signal? If it can't reproduce the full signal (full fidelity), at least in the unit I had, I don't want it. Maybe the speaker simulations were skewed because of the rolloff of the highs??
I didn't try it with anything else. I bought it primarily for my steel guitar. Its gone, dropped off at UPS this morning.