Having Midi Thru is not the point... most midi equipped instruments have a Thru port.
The point is, that the instrument not only redirects the incoming midi data from the In port, but also sends its own midi data to the Thru port. Not every instrument has this option. If the RD-8 cannot do that, Arion316 could for example not sync the Prophets clock to the RD-8. The RD-8 must do the software merge to have it working as I suggested in my post above.
I know instruments that can do this internal merge. But I would guess, that most instruments can't.
If you decide to buy a Midi Merger choose one with an dedicated power supply. They should work with all instruments.
I see...I've got the midi controller keyboard playing the P6 now as its plugged Midi out into the RD-8 in. Rd8 thru to the P6 IN. Everything playing individually but not synced yet. Either what you're saying is correct and it's not sending data out the thru port or my Global settings or RD8 settings need to be adjusted. I've got the P6 midi channel set to ALL and Midi clock set to In. When I start the drum machine the P6 sequence doesn't start and when I hit play on P6 nothing happens. I will read the RD8 manual
RD 8 says - Pressing the SYNC button multiple times scrolls through the 4 Sync option available.
1. INT (internal) – The sync is set by the unit’s internal clock.
2. MIDI – The sync is taken from the MIDI IN port. A MIDI start message is
required in order for playback to start.
3. USB – The sync is taken from the USB port. A message is required in order for playback to start.
4. TRIG (clock) – The sync is taken from the SYNC IN port. Clock start signal is required or playback can be started manually. (Sync In jack has start / stop signal on ring and clock on tip).