seems to be problematic since the packetfilter used for the proxies are set in the so called Auto-Rules - but you can try to add a packet filter rule with high priority like 'external_interface HTTP ALLOW_HIGH_PRIO ANY', add according rules for other protocols as well. Since the QoS rules are not handled by packet filters this may do the trick.
Yes, I also think this should work. Even if the packetfiler for proxies are automatically defined, a manual set of packetfilter rules for the proxies should make QoS work.
