Ah, I just looked up the Marantz. I didn't realize that they were two-channel systems. A lot of those don't include bass management or subwoofer outputs, which are very common in multi-channel receivers.
Unfortunately, your MartinLogan doesn't have speaker-level outputs, so you can't use it to filter the signal going to your main speakers. However, you might be able to get a good setting anyway. You could hook up the main speakers to the "A" speaker terminals on the Marantz, and hook up the sub to the "B" speaker terminals. You would need to adjust the low-pass filter on the sub to try and blend the sub in with the speakers. That's not ideal, but it's an option.
From your initial post, I take it that you haven't purchased the integrated amp, yet?