[Darryl Ramm]

What nonsense you talking about? "benefit of XLR signal"?

If you want to use the Solo as a DI in this setup... You put the Solo output to line level. You take a XLR female to TRS plug cable and plug the XLR end into the Solo Output and the TRS plug into a line input TRS part of one of the multi-plugs on the Mbox 3. This is the "proper" way of using the Solo as a DI, which is what your question was. If you want to use the solo as a DI you don't want to be driving a mic level signal into the ****astic preamps on the Mbox.... even if you can't fully bypass the preamps from the MBox inputs, the line level inputs on the TRS inputs should let you get more color out of the Solo. And the TRS inputs don't have phantom power on them. If you want to use the Solo as a preamp for the Mic then use it for that, it might be the best choice. But that's a separate question that you asked and you don't need to do that for the reasons you seem to think.