Ok, it works perfectly, no issues at all with the MB339 or any of the aircraft and maps I tried.
Reading other posts it looks like the possibility of pairing a TCN receiver with the DME from a VOR was introduced with 2.9, anyway it works like a charm.
In some maps, like South Atlantic and Sinai, the channels are shown after the beacon frequency, otherwise a table like the one IvanK posted is a must have.