Good point re 34a, strangelybrown. I must admit I hadn't noticed that!
6a Robust hunter nasty about fox initially needing rest (4,6)
w?l? s?i?e?
WOLF SPIDER (= robust hunter. No, me neither,) Nasty about = WOL (LOW reversed). Fox initially = F (first letter of fox). Spider = rest (as in a rest for a snooker cue).
16a Enchantress keeps sum for conversion with pirate bound (12)
CIRCUMSCRIBE. Enchantress = CIRCE (as in The Odyssey). Sum for conversion = UMS (anagram of SUM). Pirate = CRIB (as in copy or steal).
Thus: CIRC(UMS)(CRIB)E.
Hope this helps!