Preferred Method of Sub Hookup

This is my first post here so be gentle. I looked through pages of forum thread and could not find an answer. I have lurked here for months and finally registered.

I just picked up a Marantz 7300OSE which will be used with and B&W ASW600 and B&W 603s. I have had the sub hooked up with the high level outs but now that I have a decent receiver I want to use the low level out. The Sub out is a single coax but the B&W has a L and R RCA Input. Do I use a Y cable or is it OK to just hook it up to one side?

Does the manufacturer recommend? I know that with my REL sub, the high level is the preferred way.

I have had other subs which specified use of one specific channel for input from a single output, if you need to go that way.
The crossover filters in all subs are very poor, even Velodyne. I would avoid them if you care about the sound from the front left/right. I use no crossover at all on my reference system. Just adjust the sub roll-on to mate well with the left/rights. If you must have a crossover, then get an external one, such as the Snell that I have used in the past. Very quiet and virtually invisible audibly.