Just wanted to share a tip with you.

I have DTFR600 rims and Continental 2.4 Rubber Queen tyres. A match made in hell! Many snapped tyre levers and skinless thumbs later, a friend suggested changing the rim tape.

I had been running 22mm Velox cloth tape, and changed for the thinner, narrower yellowish Stans plastic stuff. Just wide enough to cover the spoke holes. The difference is incredible! The tyres go on easily now. The rim tape had just added enough depth all the way round the circumference of the rim to make the tyre too sung. Even when I tried putting the bead down in the well of the rim, there just wasn't enough give in it, but now no problem.

Amazing what a big difference the thickness and width of rim tape makes to the internal diameter of the rim!

So, struggling with fitting tyres? Try changing you rim tape to something narrower and thinner. Stil does the trick, but makes a whole lot easier!!

I have some Shimano road wheels that had tape that sat across the rim instead of sitting in the channel.
Ironically that was yellow plastic, the narrow clothy stuff sits nicely deep down inside the rim and tyre fitting is a breeze again.
Edit; Guess that's why it comes in so many widths.

Exactly the problem that I had. Because of the wider rims, everybody recommended the wider 22mm velox tape. Actually, all you need rim tape to do is protect the tube from the spoke holes, so the narrower and thinner the better. The thicker stuff covered the entire inside of rim bed channel. Not quite up inside the hook, but not far off. In retrospect, I can't see the point in wide rim tape at all. Fortunately not an expensive mistake.

DT + conti never seems to work that well. just be glad you weren't trying tu use one of their tubeless kits!

I had a similar problem, velox rim tape on 355's. I change tyres a lot and the velox tape made changing a total pain. Took it off (it was falling off anyway) and just used insulating tape wrapped around the rim a few times instead. No problems since.

http://www.schwalbe.co.uk/shopdata/files/TechInfo2-GB.pdf
Pages 26 and 27