Two DA7 mixers can be connected together in a tandem arrangement, with one being the master and the other the slave. This is done by installing a WR-TNDM card in Slot 3 of each mixer. The following is what I can determine from the manual without actually having tried a tandem connection of two DA7s.
Functions controlled by the master, not on the slave:
- Main LR Levels
- Main Aux Send Levels
- dither for LR out and Aux Send 1/2
- metering of buses and aux sends
- metering of buses, auxes, LR, Mon A on bridge
- scene memory read/write
Functions active on both mixer surfaces
- Channel Operation
- aux sends (still only 6; they're merged)
- Channel lib
- EQ lib
- Dynamics lib
- Channel select/protect
- Channel select for event editing
- Digital IO for slots, including dither
- Channel select/protect for scene recalld
- Crossfade time between scenes
- Aux returns (separate returns on each mixer, total 12)
The following weren't mentionein the manual, so I'm guessing they are active on both mixer surfaces.
- fader layer switching
- custom fader assignment windows and settings
Library sharing wasn't mentioned: are the EQ/dyn/channel libraries shared or separate on master and slave? It would be convenient to have the slave use the master's libraries. Having separate master and slave libraries would offer more options, but keeping them in sync would be annoying.
It appears the tandem linking was done right. You end up with a double-wide mixer, and the slave operates pretty much like a channel-expander module. There are twice as many Aux returns too.
You have to remember to route a BNC Word Clock cable from the master to the slave — you don't lock both mixers to the incoming clocks on their respective digital IO, because the clocks would be coming from different sources. Instead, you lock the master to whatever clock source you want (DIO slot or BNC in), then send WC via BNC to the slave.
The manual also shows MIDI Timecode (MTC) sent through the slave to the master, though there isn't a mention of how one would route timecode when using the WR-SMPT card with SMPTE LTC.