That 435 will do a fair job in my opinion, but you won't be getting all that your speakers are capable of. That doesn't mean they won't sound great, just that they could sound better. The best guy on this site to answer this question is Buckeye as he has a similar setup. You should PM him and ask him directly, he won't mislead you. I think what he'll tell you is to jump all over the speakers and receiver. You can always save for an amp at a later date. Essentially you'll be getting a system that sounds great now, and that you can make sound even better later with a simple addition later down the road. What is the price on that Velodyne sub from work? If it's under $250 I'd consider it a top contender unless you are willing to save for a brand your store doesn't carry. That Velodyne looks to hit 25hz with some authority, but for $429 plus shipping you can get a SVS PB-10 that can hit 20hz. You really don't want to skimp on a sub. I did originally, and now I'm saving to get something half decent.
Finally my suggestion is this. Take the Harman and hook it up to those speakers while you're at work and see how it sounds. I bet pretty good. Also remember that even though those Polks are power hungry if you are using a powered sub then you can set a higher crossover on your receiver. That means that the speakers won't be producing bass as deep as they can and that means they won't be drawing as much power from your receiver which means you'll need slightly less power. Like I said PM Buckeye, but I really think you're on the right trail.