I tend to agree about the BT & WiFI conflict. You might test the theory by turning off WiFI and seeing if local file playing sounds better. Some headsets might work better than others but the N8* itself suffers with the two radios being that close physically. My latop has an internal BT module and it is physically at the far corner from where the internal WiFI is located.

Can't guess at which headset might work better than another as I am less than impressed with BT in general and find most BT pretty crappy compared to a cable.