If you want long term gloss then Shellac can be hard to beat, spalted wood can be a bit punky so it tends to absorb quite a lot, but if you are patient and wait for it to properly dry between coats it will soon tighten up. I would apply a fairly heavy base using about equal amounts of shellac to spirit or slightly less spirit, this builds up well if you have very absorbent areas, once you have an overall covering, spend time cutting it all back with some 400 grit to get a good smooth surface, then apply further coats of a slightly thinner mix with a rubber till it has built up a sufficiently deep coating (not too deep, but enough to withstand the next step) leave to dry for 24 hours in a warm dry place, then remount on the lathe and use buffing compound with a soft cloth to gently abrade the surface to a high gloss. You don't need the lathe to spin too fast, nor press too hard, let the compound do the work. Chestnuts buffing compound is great for this, you get lots in a bottle too. I also use water to lubricate the cloth during this stage.
Once the buffing is complete, polish is with a dry cloth, no need for wax or any other covering.
You can also use the buffing wheels to polish it up, use shrt light passes with the tripoli wheel, run it at about 1100 rpm, then polish with the diamond white with the wheel running at no more than 600 and just light pressure, keep it moving, if you sit in one spot it will quickly heat the shellac and melt it causing a drag mark, which will definitely be a drag! (fully intentional pun!)
