ill post some other options besides my idmax out for you. ive heard all (unless stated) or personally owned them.
Fi Q or Fi Q with bp option. without bp option a fi q could take 1200 - 1300 so long as the top end frequencies was below 70. Owned personally in the same ported box of mine i used with idmax and it sounded fantastic. Very powerful lows. but nice stretches up throughout 60's, drop off around 70's
JBL W12GTI - Heard can take 1200, Very nice driver that off specs and parameters does well in larger boxes or applications, IB, Large Ported. even large sealed
Older Stereo Integrity mag versions not the new one coming out can take 1200. These subwoofers fit in my top 3 sq wise, and is very impressive across wide range of frequencies. neutral flat sq response, excellent lows, blends well, works in variety of apps. behind subs like rainbow vandiums, and an aura sound setup i heard well over 800$
another big wattage very good sq sub up and rising i havnt had a chance to hear yet. I read npdangs review who is a very reputable speaker analyzer and reviewer for us over at
diyma.
Very very bottum heavy subwoofer that can take loads of power id say 1400, flat neutral response but should be limited in the 60s when crossing over. nice ported response.
hope this helps. i understand im putting some draw backs and situation with you. ill let you know when $$$ issue is straightened out.
Mike-