One caveat to Per's suggestion:The GR-55 will need to be the word clock master in order to prevent clicks and pops due to unsynchronized audio.
In the past, I've had problems with random latency when using an aggregate audio driver.
On Apr 3, 2012, at 7:37 AM, Per Boysen <email@example.com> wrote:Hi, This is a tip for those using a Roland GR55 guitar synth and a Apple computer for amplification/recording. The tip is that you can pipe the GR55 into the Mac digitally through a USB cable without having to set up the GR55 as the external audio interface for the Mac. Many good audio interfaces sound better then the GR55, both on the input side for digitizing the guitar's analog pickup outputs and on the output side when sending the mix to monitoring or PA. By going digitally through USB we are sidestepping the lousy AD/DA conversion of the GR55 so you get the GR55 synths as digital line-in and still can plug your guitar etc into the better audio interface you hopefully have. This means the GR55 is active as an audio interface together with your normal interface and on a Mac and you can make this routing possible by creating an Aggregate Device in the Audio MIDI Setup Utility (look for it in "Applications/Utilities"). Under the audio tab you click the little plus signe down left and create your own Aggregate Device where you can combine many physical interfaces. In my case over here I'm combining my RME Fireface400 with the GR55. Now, when launching an audio application (like Mobius standalone, Logic, Live...) you open its preferences and select your new Aggregate Device as its audio interface. In my case what happens then is that the audio application detects 20 incoming channels instead of the usual 18 of the RME box. Channel 1 - 18 are the usual RME channels while channel 19-20 is the USB stereo feed from the GR55. The sound is much better compared to when I used analog guitar cables from the two GR55 outputs into a stereo input of the RME. And less to schlepp around. Greetings from Sweden Per Boysen www.perboysen.com http://www.youtube.com/perboysen