I found a solution to the problem of high sidetone volume in the DCxxB series transceivers. Parallel to R23 on the board there is a space for a resistor labeled R21 which is not used. This runs from the junction of R23 / C27 to ground. You can put a resistor in there to form a potential divider. I used something like a 47K to get it down to a level I was comfortable with. Quite why this is omitted from the kit I have no idea.
However, I also seem to have discovered a bug in the keyer! (Why is it always me that finds the bugs??) I found how to get the memories to replay. You need to key dot or dash on the paddle milliseconds after pressing the function button. The recorded message then replays, but though it sounds fine on the sidetone only the first symbol of each Morse character (or something like that) is actually transmitted. What you hear in the receiver is the odd dit or dah, with long pauses in between!
Chuck, W5USJ, on the dc40kits Yahoo! group, has suggested that to get the rig transmitting and receiving on the QRP frequency I need a 10uH or 15uH inductor in series with the crystal to pull it down a kilohertz. Really, when buying a kit I didn't think I'd need to perform several modifications before the thing would work properly. I don't have any inductors of the right value, it's going to be a challenge to fit one in, and I'm not sure the DC20B is really worth the effort.