older rockford fosgate stuff isnt bad. look for the IX series and you'll be good to go. you can usually pick one up on e bay for around $150 and will run about 700 watts at 2 ohms. i had 4 of those amps and 4 fosgat power dvc subs in my 93 mustang and they never let me down. they didnt even clip or shut off. the thd% isnt bad either. you'd be looking at less than 1% thd at 2 ohms.....lots of clean power.

 

SSF in those fosgates? anyone know when SSF became common in amps? do you really NEED it for a ported box? im sure theres some sort of external device that does the same thing.....maybe not....

 

the older fosgate amps have a cross over card the depending on how you install it you will get full range, highs, or lows. you can actually swap out the cards for different fre. responces but the cards are hard to come by. the only other settings are bass and treb. so i guess....no they dont have a subsonic filter built in.