| Yeah I don't think the duet has insert points. You'd have to either put the hardware first, on the way in, or add it later by coming out of the duet and back in again on the line in's.
Processing on the way in is very common in professional recording, but does require some balls to say 'yup, that sounds great and I'm NOT going to want to change it!'. Not advisable if you are not very confident, but is a great commitment to make early on in tracking if you are up to the task!
Coming out and back in the soundcard will degrade the audio by a generation. Not too much of a worry on the duet but worth being aware of, you want to keep conversions to a minimum really. Also, you will get a bit of a delay on the return audio and you will have to line it up with the original, this is easy enough if you use a very transient 'click' on a spare bit of the audio track to be sent to the fx boxes. Record this click along with the audio track and then you can line up the return audio with the send very easily.
Note that depending on what outboard you are using you will have to consider further things. For example most rack compressors expect line level, if you are using the apogee's pre's then there is no way of going through them then into the compressor then back to the apogee in realtime, you'll have to do it later. If you are using an external preamp then you can line up the gear however you want before hitting the duets line-ins at the end of the chain!
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) and then go back into the comp you're converting the signal twice more and ultimately degrading it (unless you are mixing analogly or summing, in which case it's worth it)
