Two SQ 12's

[Two SQ 12's]

Image dynamic subs are great for sq either the IDQ or ID Max both would sound great with nice output

[Audioque amps]

Audioque amps do actual power and the ratings are at 1% distortion or lower. Most amp companies like fosgate and hifonics usually rate their amps over 1% which could mean at 3%,5% who knows. I have played with the Audio3500 amp first hand and it is a great amp that does a little more than rated.

[Sundown or AQ?]

Both companies have great customer service and also sell a great product. I have done testing with the Audioque 3500 amp and the Sundown 3000 and the Audioque was .4 db louder. Both companies do underrate the amps so It is just really a matter of style and power difference probably in this case.

[subwoofer: Audioque HDC315 vs RD Alpha v2 15" D2]

I don;t know about the RD Alpha sub but I just got some of the Audioque subs for a demo vehicle build and it those things slam. I am running a audioque 3500 per sub at about half gain.

[Extra power?]

You should have enough power to run that with no problem but I would not use the cap if I were you. Every test I tried using a cap it hurt more than it helped.

[Four AQ SDC2.5 15"s]

Why not just stick with the Audioque amps as well, they put out full rated power and the price is great too.