Axiom did some blind listening tests, and the 350 actually did very good, almost matching the 500 in many respects, since they updated the amp about a year ago. With that said, the 500 has DSP and a bigger amp, so it will play louder and lower. Depending on how you use the sub, you may not see a huge difference.

I have 2 350's and an EP600 for intense bass.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85