Following up to my own note, if you just want to do button presses, then
you won't have to do an 'open' first; rather, you can just do a 'send
message' command.

To confirm that sysex can be received OK by the host, from the Polaris
do a LF-C-12. This should perform a "send main workspace program out
over MIDI." It will do this via a sysex message.

You'll see something like:

190905 F0 08 01 4F
30 30 38 35
30 31
190909 F0 08 01 57
32 43 30 30
30 30 46 34
30 30 31 43
30 30 30 30
30 30 30 30
38 30 43 38
41 45 30 36
43 38 31 37
38 36 35 31
30 30 30 30
30 31 30 30
41 30 30 31
46 43 30 44
30 35 46 38
30 31 31 43
38 30 46 46
30 36 30 30
30 39 31 38
30 30 30 30
30 31 30 36
30 30 30 30
31 38 30 36
30 32 37 35
31 46
190947 F0 08 01 53
31 45 30 30
37 46 30 30
F7

Using the MIDI Implementation manual to decode the stream will give you
a good felling for how the Polaris decodes/encodes sysex.

Of this dump, the last portion is the most interesting for your original
question. It has:

190947 F0 08 01 53
31 45 30 30
37 46 30 30
F7

Decoding the stream we have:

F0 08 01 = start of sysex, fender ID, channel # (in my case, the MIDI
base channel was '2').

The Polaris uses ASCII strings to represent data - so for the first
message we have:

53 31 45 30 30 37 46 30 30 F7

0x53 = ASCII "S" = Send Message.

A 'send' has the following format:

Sssiimmoo

Where S = ASCII for 'stream'
ss = stream number
ii = instrument number
mm = message
oo = operand

For this example, stream number = 1E (instrument stream)
instrument number = 00
Message = 7F
Operand = 00

In your case where you'd like to change the value of a switch, you'd to
'send' to a stream. Stream 16 is the panel stream.

So that would be:

F0 08 01 53 31 36 30 30 30 43 30 31 F7

Where:

53 = ASCII for "S"
31 36 = stream number "16"
30 30 = instrument number 00 (ignored)
30 43 = "0C" = 'switch press' command
30 31 = "01" = switch #1

So sending this command should 'press' switch #1 (The sequencer 'stop'
button). Changing the switch number (the last two bytes) will allow you
to press any/all buttons on the Polaris.

A similar syntax can be used for slider moves.

Be sure to let us know how you make out.

David