I have a Mackie Onyx 1640 (not the i-series). Once I get raw tracks recorded in Ardour, is it possible to send Ardour tracks through my Mackie’s aux send busses to processes them with an outboard effects processor? I don’t see a ready way to do this by looking at my available connections in Catia, but I’m hoping there’s a way I’m not seeing.
The Mackie Interface gives 18 Tracks in a DAW and 2 Tracks back. The only to way bring the 2 return tracks back to a channel strip and into an aux bus of the mackie, is to route them in the monitoring section to the main out and patch the signal from the main insert into a channel input again.
Btw, don’t forget that you can daisy chain firewire devices because of it’s bus architecture. So for monitoring or outboard gear I use the edirol fa101. It uses the same ADDA chip as in the mackie cards but for 10 AD / 10 DA. So you have 8 analog out for free routing into the mixer again. The edirol fa 66 with 4 out should work too. So with my two mackie 1640 and the edirol fa 101 box I have altogether 44 analog IN and 12 analog out in use with ardour 
Hm… Thanks for the excellent suggestion, iluam. I actually have a 1620. I just cleaned up and rewired without the 1620 in the mix, but this might be an excellent way to use my now “spare” 1620.
OK, looked over my Mackie and patched the main insert into a free channel strip, but I’m not getting a signal on that strip. I’m sure I’m overlooking something…
I also tried patching the control room out to a channel strip, but again, no input on the strip even though the main meter is showing a signal.
Check first that the right signal is routed from ardour to the mackie. You have to “enable” the firewire IN tracks in the control room section of your mackie with the button labled “FIREWIRE (Option)”. It’s regulary just for monitoring purpose and so the signal is routed to the control room OUT and the PHONES jack. So if you hear your sound from ardour now, the first step is done. If you now want to redirect the signal into a channel strip, you have to press the button “ASSIGN TO MAIN MIX” and it’s routed to the MAIN OUT too. Then you can grab the signal from the MAIN INSERT. But keep in mind that every insert jack is a stereo jack (tip=send, ring=return, sleeve=ground) . So if you just want to grab the signal, take a cable with a mono plug and insert it only to the first “click” into the MAIN INSERT jack. (So it works like a “direct out” without interrupting the main signal on it’s way to the MAIN OUT jacks. Look on page 21 in the mackie onyx 1640 owner manual for clarification.) With this cable you can go to a LINE IN of a channel strip. Of course don’t route this channel to the MAIN MIX again! But if you just want to feed outbord gear, go directly from the MAIN INSERT into your outboard device and redirect the output into the mackie again.
I spaced on inserting the cable properly. Thanks for the reminder.