@SCC
As I see it, the Hp device will be transparant .. so the MX port should act like a single voice device was attached (with exception of single MAC filter, since multiple MAC's will be comming in)
So my input will be to go for Access config (in the correct VLAN), and remember that when leaving the MX, no QoS will be executed since the unmanaged HP device will not know how to queue.