One way is to route your recorded track(s) via either of the Send outputs to your external FX, then feed the FX output back to another input on the DP32 and record it. The Sends are controlled via the Mixer screen - select the reqd. track and confirm this is displayed on the top right of the mixer screen, then set the Send to Pre or Post as reqd, set both the Send level for this track and the Master Send level. Repeat for any other tracks you want to add FX to. You can check the routing is correct by using Monitor Select to listen to the Send bus which you've chosen to use. If you can hear your track(s) then you know there's a signal going out to your external unit. Don't forget to reset the Monitor Select back to the Stereo bus if reqd.
You can use either of the two Send outputs, but if you use Send 1, this also goes to the internal FX. This won't matter as long as these are off, or their Return level is set to 0. If in doubt, use Send 2. Hth.
