The IDMax is a great sub, and provides more bass and SQ than any normal person will ever need. The IDMax ,IMO, will outplay 2 IDQs, but as of lately the IDQs have been going very cheap on ebay. So cheap, I considered putting them in a setup that I am building for someone for SPL. IDQs put out very high numbers and work in the smallest of enclosures. AS you said, you are in a win/win situation.
Semi Retired SPL Master
Review Commitee Organizer
Team CarAudio.com Captain
2003 NSPL Regular Cab Record Holder
Big Thanks to Loyd Lowry and Nick Lemons from Stereo Integrity