[Topic moved here.]
Are you sure you mean page 153? That's the 'Stop/coupler/tremulant switches and pistons/buttons' section in the current (v4.2.1) version of the Hauptwerk user guide. (If you have an older version of Hauptwerk installed currently then please first upgrade to the current version: http://www.downloadhauptwerk.com/ ... which is a free upgrade.)
From your description, I assume you're referring to the 'Organ settings | Advanced MIDI applications | Direct MIDI input/output for ranks/pipes' screen (page 158 in the current v4.2.1 version).
solotibia wrote:When the option to drive external pipework is chosen does this mean that the virtual rank that it is to replace is switched off? Or would I have to not load the virtual rank for this to occur?
You would also need to disable the rank via the 'Organ | Load organ, adjusting rank audio/memory options/routing' screen in order that the virtual rank no longer sounded within Hauptwerk itself.
solotibia wrote:How many ports of MIDI would be required to eventually cope with 10 ranks of unified pipework - 706 pipes?
For best results (tightest timing) my inclination would be to get as close to one MIDI OUT port per rank as feasible, on the smallest number of MIDI interfaces possible (keeping them all attached to a single good-quality [e.g. Belkin] *powered* [not 'bus-powered] USB 2.0 hub if more than one MIDI interface, to avoid any potential for issues with them getting switched around in the OS). E.g.:
- MOTU MIDI Express 128, which has 8 MIDI OUT ports: http://motu.com/products/midi/128 or:
- iConnectivity Mio 10, which has 10 MIDI OUT ports: https://www.iconnectivity.com/products/midi/mio10 .
They're both rack-mountable, which is very handy.
I have several MOTU MIDI Express 128 units all connected via a single Belkin powered USB 2.0 hub and they work very well for me on both OS X and Windows. I have no experience myself with the iConnectivity interfaces, although of course having 10 MIDI OUT ports on a single interface could be an advantage.
Probably the slight loss of timing resolution (and additional latency) from having two ranks share the same MIDI OUT port (e.g. on a single 8-port interface) wouldn't be considered noticeable anyway, especially if you picked the least timing-critical ones (e.g. ranks with slower speech).