Setup using Denon AVR-4520CI with Bel Canto 300i (D) and 2 Velodyne DD15 subs

Haven't been on for awhile and probably don't use correct terminology, but here goes.

I have 2 Velodyne DD15 subs, one being the "plus".
They have speaker-level inputs (not outs) and line-level inputs.
You can use these subs with two completely different systems if you prefer ... one hooked up each way.

Main speakers are Revel M22 monitors.

I'm wanting to use the Bel Canto integrated (300iD) for 2 channel listening and then it can be "passed thru" the Denon AVR-4520CI so I can use it (and the connected Revels) for surround fronts.

Question I have is, how do I hook up the Velodynes so that I'm only running 80Hz on up thru the Revels and not using them full-range.
If I use line-level inputs thru the Denon, that's easy ..... but then how do I NOT run full range from the Bel Canto?

I've seen some subs with 4 sets of speaker connections (2 sets in (R&L) and 2 sets out (R&L)) for each channel so you can run speaker wires into subs from source, and then back out to monitors and use sub crossover.  But these subs only have two sets of speaker-level in connections (R&L inputs).

I'm sure I've missed something, but wondering if someone can help?  Will I have to have an outboard crossover?