Analogue-sequencer

> Same here.  When you send the 55, should you see anything anywhere - 
> either on the P3 or the MIDIOx screens?

Make sure you can see both the input monitor and output monitor windows in
MIDIOx, have the PC ouput connected to the P3, and the P3 input connected
back to the PC.
When you send the '55', it must be sent as a single byte - without any F0 or
F7 around it.
You should see the 55 sent, and echoed by P3 as in this image:
http://www.sequentix.com/images/MIDIOx.jpg

If you don't see that, it's possible that MIDIOx is filtering the byte, or
isn't configured quite right.
Make sure MIDI pass-through is not active - in the "Options", "MIDI
Devices..." window, turn off "Automatically attach inputs to outputs during
selection" and make sure there are no input ports shown in the 'port
mapping' for the output port.
Also make sure 'MIDI-Ox Events' are mapped to the output, like this:
http://www.sequentix.com/images/MIDIOx2.jpg

It's also possible that your MIDI drivers will refuse to send a MIDI message
without a status byte.
You could test the connection by connecting the MIDI output on your PC
directly back to the MIDI input, and see if the 55 is sent and received.

Best regards,
Colin Fraser
Sequentix Music Systems Ltd
http://www.sequentix.com