the alpine cda-9857 allows you to bypass/disable the internal amplifier, which should allow for a direct connect to the Bose system without the need for converters, etc.

I already have an infinity basslink in the trunk, but it's connected via taps to the rear deck speaker connects. I'd love to be able to deliver a clean signal to the sub straight out of the HU via RCA, preferrably something with volume control.