Have you considered a pair of LE12's in a 2ft^3 box? They would be perfect for your current amp at 300w each. You could sell your IDQ's for near their purchase price and then build a box for around $30.
My LE12 plays much, much deeper than my IDQ10, more than I'd expect from a larger cone area. I don't think you'd be disappointed.
I'm guessing that output between the LE12's and IDQ12's would be comparable with maybe a slight edge towards the IDQ's, but the LE12's would play deeper.
In any case, have you thought of just trying the IDQ12's in a larger box? It should improve their low bass response, 1.1ft^3 for a pair of 12s is tiny. They must have a really shallow mounting depth to fit 2 to a box that small.
