The BR 864 is definitely worth the extra bucks man! Hands down. For one the mr-8 has no eq's so u cant shape the sound at all no rhythm patterns. the Boss features bass simulator, drum machine, killer effects, eqs..etc and sounds awesome. If you record solo ...... the bass simulator, and drum machine is useful.
I agree, the Boss is incredible. It's really easy to use and totally fun. It's got 24 bit preamps and a usb output so you can import wav. files to your computer.
