So I got a Yamaha DXR10 yesterday, after reading tons of posts on here and elsewhere (axe fx users). Plugging right in, no messing around with EQ or anything, it sounds fantastic. I used one of the main outs (XLR) to the XLR input of the DXR10, had it set to "Line" like Pick909 mentions above, and had the D-Contour switch set to 'Off' like saw someone else mention on here. I could hear some elements of the sound of some profiles that I had not heard using just my studio monitors (KRK Rokit 5s). Maybe that was because it was turned up much louder. So, I'm very happy with this (I only bought one). BTW, I got a great deal on it - bought it used from Guitar Center for $399. So search on there and try to find one, as they'll take the order over the phone and ship it to you, and you can still return it locally if you want. Obviously this applies to those of us in the U.S. only.
Also, some people on here have tried the Fender Mustang III as a monitor (by plugging the KPA into the effects return - I bought a Mustang III (V1 - you have to use the Version 1 of this), also used from Guitar Center, and tried it a couple weeks ago. I did all the tweaks that people say to do, and had the cabinets turned off in the output and all…and I was underwhelmed. It had a screamy tone to it, kinda made my ears hurt. And I figured I didn't want to have to be tweaking the hell out of every profile to make it sound decent, so I went the faux-FRFR route and got the Yamaha DXR10 after reading so much about it and seeing it in the store.