Any ideas on how to use an old Express console to output MIDI to a more modern console?

Express will only output MIDI in response to specific events. According to the manual these are:

MSC commands transmitted by the console MIDI Show Control (MSC) allows the console to send the following commands to MIDI devices. If MSC output is enabled on the console, the console automatically sends the MSC commands. The console's transmitter Device ID must match the device ID for the MIDI device receiving the signals.

[A/B Go]

• If a cue is pending, the console transmits [A/B Go] with cue number and a list entry of 1.
• If a cue is holding, the console transmits [A/B Resume] with cue number and a list entry of 1.

[C/D Go]

• If a cue is pending, the console transmits [C/D Go] with cue number and a list entry of 2.
• If a cue is holding, the console transmits [C/D Resume] with cue number and a list entry of 2.

[A/B Hold]

• If a cue is running, the console transmits [A/B Stop] with cue number and a list entry of 1.

[C/D Hold]

• If a cue is running, the console transmits

[C/D Stop] with cue number and a list entry of 2.

Macros • For macros 1-127, the console transmits Fire with the macro number.

So assuming you get Express to send these MIDI messages then your modern console would have to respond to them.