i have a SS 1500d

1500rms @1ohm
1100rms @2ohm
800rms @4ohm

do u reckon 2 SS reference 12's (dual 4ohm) would be underpowered by this amp???

I'm sure 700w per sub will be adequate.

They're rated at 600, so yeah 700-750 is plenty. Theres a guy cruising Ballarat with one PCA1500 and two older RF woofers, the VanGoghs, and they sound good in small sealed enclosures. I have, until recently, run two PCAs and 4 x SPL12s (now as part of setup for member TBASS). What type of enclosure are you working with?

but they have a 4 ohm impedance

If you were to wire each sub to a 2ohm load, then parallel them down to a 1ohm load at the amp, you will get the most from the amp, and matches your subs fine.

thanx guys