You can plug your Aguilar's Preamp Out or Effects Send (I am not sure how the jacks are labeled on that model) into your Acoustic combo's Effects Return jack using an instrument cable. This will safely allow you to use the Aguilar's preamp capabilities with the Acoustic's power amp and speaker.
If you want to bypass the Acoustic's power amp entirely, and use the Aguilar as both preamp and power amp, then check whether it has an easily detachable cable as in the photo above. If not, you'll have to do some surgery on your combo---are you comfortable with that kind of thing?
(edit) I just googl'ed the Aguilar and it appears it does not have a post-EQ 1/4" output (just a Tuner Out which is probably pre-EQ---can an owner confirm?), so ignore my unenlightened comments.