Forget about the HW-decoder. MP didn't use it, becuase the output of the decoder is pure video without MP GUI. Much more important is the encoder, both cards have it build in and so you get smart recordings without any stutterings. Becuase the price difference between 350 and 500 are not that much, I suggest to buy a 500. Also if you think you didn`t need the second tuner, believe me, you use it and you love it
Remember that the 500 has no remote control, so you have to use another remote solution.