Ok, turns out I have no idea what I'm talking about when it comes to amps and amp effects. So after a little research, I think I have a better idea of what's going on (but not how to fix it).

In my first post, I was trying to hook up the delay pedal in the effects loop (after the preamp and before the power amp, right?). I tried hooking it up before the preamp, and it works and is at full volume. But I read that, generally speaking, people put delays in the effects loop. Why is my effect loop volume so low (I don't think I have a volume knob specifically for it like some apparently do)?

Not sure if its the effects loop that is really low or the fact the Giga delay isn't putting out a line level output, but a guitar level output. I'd guess your send is expecting a line level return from rack-type gear, but the Gigadelay is sending a guitar-level signal. Without looking at the manuals for the amp. Either that or your amps effects loop has something wrong with it. Either way you should be fine the way you are now.

It looks to me like the insert is setup for guitar pedals. From the manual:

EFFECTS SEND
1/4” output jack for supplying signals to external low-level effects or signal processing equipment.
EFFECTS RETURN
1/4” input for returning signals from external low-level effects or signal processing equipment. This is a
switching jack. Inserting a plug into this jack will break the signal path until it is returned via the
EFFECTS SEND (#13) jack.

Effects Send:
Low Impedance: High-Z, 22 kΩ
or greater
Nominal Output Level: 0 dBV,
1.0 V(rms)
Effects Return:
Impedance: Very High-Z, 1 MΩ
Designed Input Level: 0 dBV,
1.0 V(rms)

TBBucs, try running the guitar into the pedal and that into the return.

So...this is pretty embarrassing. Guess what happened when I switched the send/return cables? :)

Thanks for your help guys. The bright side is that I learned a little about how effects work, so I guess it wasn't a waste.

I love these AHA! moments.

I can respect that you came back to 'fess up and not leave us hanging. One of these days someone will be having the exact same problem and you'll casually point out their cabling error making you look like a hero.