My brother brought over his Lexicon and Boss pedal boards as he has certain tones set up for his guitars and when we connected it to my Presonus Firestudio Project I had know control of the volume. We tried XLR, then quarter inch jack, tried 1& 2 channel then 5 & 6 and we couldn't figure out how to get volume control. We could control the volume from his pedal boards. But that's useless for recording and mixing. We went straight in to the Firestudio project, not using a quitar amp. He says he plugs in to his Zoom R24, and other audio interfaces and has had no problem before.
Does anyone know what we are doing wrong, or is the firestudio not set up to be compatible with these type of digital pedal boards?

Thanks

Mark