Yes I would be prepared to wait a month though I agree with what Ian has said. With a 502 I would try to find the extra to go for a 557. Prior to my first DSPs I had an extended trial of a 502/557 combination and it was very good. For me they sounded better than the DSPs I ended up buying - at the time the convenience of the DSPs swung the deal.

If you stayed with your 501 however then a 556 would be ideal.