The dd will get louder by design and it has more cone area than the two AQ 10's. Plus you wont need as much power to get loud because its rated 1500 rms. I wouldnt run 2800 to it daily.
i already have a 9515 running on 2800rms with no problems at all. im looking to switch to something that wont take up quite as much room which is why im interested in the 10's. Im getting a new vehical and if i could keep the 9515 i would but there isnt enough room so how would 2 HDC310's compair?
If you really want to save space go with a single 12 with options if you want to give it some power. My brothers tenant has a hdc 12 in about 1.75 cubic feet net each tuned to about 37 hz and it sounds good.
I heard the old audioque 2.5 12 and the digital designs 2512 and they are very similar in sound. The audioque hdc 12 can sound a little sloppy on the low end in a low tuned box (35 hz) at 2.50 cubic feet but in my brothers tenants box it seemed pretty tight. In an spl box the audioque hdc 12 did a 147. something for us on a good bit of power and the dd 3512 was at like 145. something at like 1200-1500 watts but im thinking the 3512 would have done about the same numbers if we had more power on it and in the right box. The only time I heard the 3512 in a daily setup was in a wall with like 6 of them in a small car and it sounded like it hit all the notes pretty good from that I would have to say the 3512 probably has a tad better sq.