Problem with outboard effects


this might be a stupid question, but how do you guys incorporate outboard effect units into your workflow? I own an audio interface which has onlyone output and I connected it to the input of the effect unit and the output of that unit to the line in of the interface. In Renoise I use a Send Track followed by a Line In to send the signal out and receive it again, but logically I now hear a mix of the original signal + the processed signal (as the output is connected not just to the effect unit, but also to my headphones).

It follows that I also have to deal with annoying feedback in some cases. An inconvenient solution would be to use another pair of headphones just for the processed signal, then sample it and use it in Renoise. But there’s certainly a better solution for this out there.

How do you guys solve this problem without having to use an Audio Interface with several Ins/Outs or a mixer?

Thanks in advance.