I have run RE SRX and Infinity Kappa 120.9w 12 inch subwoofers (one at a time in a sealed box) in my sedan on 250watt RMS at 2ohms channel and I never felt that my car lacked sub bass output. 10 inch subs on 500watts RMS should get decently loud. Both are really nice subs, specially for the price.
By the way, another interesting option is to have 2 Dayton Reference HF 10 inch subwoofers. They need approximately 0.75 to 1cu ft each. They have very good sensitivity, which is always good. I would always worry about subwoofer sensitivity if it was to run off a Class A/B amplifier like yours. More sensitivity == less power consumed, cooler amp. I have done some models in WinISD, and a dual HF10 setup has 3dB higher sensitivity compared to dual Infinity Kappa, which is remarkable. They need half the power of Kappas for the same SPL.