Help to sync Transport's object @clocksource to ReWire

Hi everybody,
I've tried to sync the transport's clocksource to rewire, but never managed to do it successfully. In the documentation, it is said that the Transport object can be clocksourced to ReWire...

As soon as I put "@clocksource ReWire" in a transport object, it just ignore the start messages and refuse to output his data.

I've made Max7 rewire slaved of Renoise without problem and the rewire clock is well received as I see the "hostsync~" objects giving numbers on his outputs.

After a while, I guessed that maybe the sourceclock just can be provided by Max in ReWire master mode, so I've set up Max to be Master, and Renoise to Slave, but as well the transport object does not want to be assigned to the ReWire sourceclock.
Anybody have a clue on how to make it work?

The main goal is to have a very accurate clock from one or the other to shoot back midi data from Max7 to Renoise...
Other solutions could be to send a Midi clock from renoise to Max7, but I actualy don't know how to unpack the midi clock's data. Or to send a self-made midi clock from Max to Renoise, but I don't know how to do it as well.

Thanks in advance,
Cheers,
Martin