In the case of the RS 7000, it can handle multiple songs. If i switch songs, the RS 7000 sends a "Song Select" midi message to its midi out(s). Therefore the midi configuration of the RS 7000 has to be set up to transmit the midi control message to the midi out where the ST224 is connected to.
Then, if in pattern mode, switching a style, or in song mode, switching song on the RS 7000, the song will also switch on the ST 224. This will work even when the ST 224 is not in SONG->Midi->Midi Mode.
The ST224 will then also react to "Song Position Pointer", which means
that if i dial up a specific song position (eg. 4:00:000) on the RS
7000, the ST224 will also jump to that measure (This will also work while the st224 is in record mode ;))
The ST 224 will also respond to MTC (Midi Time Code) if set up correctly in the RS7000 midi config, overriding the initial BPM specified for a song and using the same tempo as the RS7000.
Therefore, the ST224 SONG->Midi->Midi Mode has to be switched on.
Sadly, the ST224 goes out of sync sooner or later if no additional "Song Position Pointer" or "Song Select" is sent (which the RS 7000 doesn't do if it loops a pattern e.g. jumps back from measure 1:00 to 4:04).
I will write some detail on using the Midi Solution Event Processor when i get a good workflow going ;)