Why does it not have a send level? I have a Triple Recto with the parallel loop and have no issues using Chorus pedals. Does the channel master double as the send level? Many amps do that. You may need to turn up the channel masters, and then turn down the global master to compensate.
Yeah, in a parallel loop, the volume is what controls the overall amount of effect. Keep the mix at 100%, and then control the amount with the volume. I do this with my TC Electronic G Major II.
Keep in mind that you cannot use a Parallel loop, and then use effects in series. So, you cant use the parallel loop, and then put Chorus, Delay, Reverb, etc... in series with each other, because none of them will work unless you have them all on at the same time. You might see if this is the problem. ONLY use the Chorus and unplug the rest to test it.
Any Chorus pedal with an analog dry-through, or a digital unit with "kill-dry" or the ability to dial the direct signal to 0 should work.