Hi George

Unfortunately because you do not control Router A anything you do will have little impact. Yes you could give priority to requests from the PC but the trouble is that the return traffic will not be prioritised.

Worse general internet surfing traffic is characterised by small requests and large responses and it these reponses which will not be prioritised.

If you suspect the blockage is at your end as the traffic goes out then it may be worth trying some QOS - i would do it on the router B rather than the Pix because IOS has a richer QOS toolset but i don't really think it will make much difference.

Jon