I have just received some third party tips for the DM6 and I am really impressed.
I got the from Amazon UK. Called TCM TORNADO silicone earbuds. I got them in the large and the fit on the DM6 and in my ears is perfect for me. The bore does not cover any of the sound tube, so you get unrestricted sound, they seem to have some sort of spiralling going on in the outer flange, I've no idea if this has any effect, but these are better than any of the stock tips supplied and the sound has improved for the better. Cost me £5.95 Prime including delivery for 7 pairs, this is a no brainer must have punt.