I've figured out how to use the Moog Modular as an insert effect http://creative-audio-production.com/2016/01/21/running-audio-through-a-virtual-synth/
But I have no idea how to run external audio through the ARP 2600.
Of the three virtual synths (in the V Collection) that act as an insert effect, the 2600 is the only one without a discussion thread in the forum.
I just noticed that for the Minimoog, somebody indicated that you needed to be playing a midi note in order for the effect to be working/heard? Maybe that's the same here?
On a similar note; is it just me, it seems like all of the presets that are EFX .... don't do anything?
I can see you have a post in modular V forum here: http://forum.arturia.com/index.php?topic=3771.msg127594#new
ARP 2600 V and Mini V works the way as described in Szlartibartfaszt post in the above thread.
Take step 1 and 2. In step 3 you don't have the option to switch off the keyboard trigger as far as i can see. It's actually on. I actually recommend you try to use the Keyboard trigger on in modular V too.
The rest is about using the external inputs like it's possible.
In Mini V the External input in is in the mixer section.
In Arp 2600 it's the preamplifier in the upper left corner.
It might be me you refer to about MINI V. And yes i do it the same way with ARP, and also in some cases in Modular V.
Just a hint. If you arm both the track with your regular synth and also the track where you have your FX synth, then you can play both using your keyboard. But you can also play different notes. Experiment.
Also just to inform others too: To get an FX plug-in on a track may involve first to add it as a insert effect or a FX send effect, and then select this FX plug-in for a instrument track.
About EFX presets. EFX is just a effect. It don't have to be used for a external input. It can just try to be water, wind, helicopters and what ever you like that is more an effect than for instance a sound you play tunes or chords with.
This is how i get things to work. But i hav'nt used it that much.
Hope this helps.
EDIT: Also remember the "ext in" possibility in the MINI V matrix.