Team Trek bike due to arrive shortly. Never had a Trek. Bike is a 6.9 SSL with the Duotrap in the chainstay. I've been told the Duotrap will work as a speed sensor for my SRM system (7900 wireless, PC7) so I don't need the bulky zip-tied pod. Is this true? Do I just pair like normal via the PC7? Oddly, I couldn't find an answer to this question easily online. Thanks, all!

Yup. I have done that for a friend with one.

@Geoff.
If i understand correctly, the BB mounted 'sensor' supplied with SRM is in just a magnet that lets the SRM unit transmit cadence.
Since the duotrap also transmits cadence does mean one no longer needs to install the SRM BB pickup ? (With internal cable routing, Di2 battery mounting, etc all going on under the BB shell , installing these SRM BB pickups has me resorting to hot glue and other hacks)

You still need the SRM magnet since it trips the reed switch, however, you don't need it for cadence necessarily. The way I understand is that the magnet ALWAYS needs to pass through the sensor pickup on the back of the spider, but you can pair other sensors as secondary cadence/speed sensors. For instance, to use a Garmin speed sensor you have to pair it as a Duotrap, etc.

The SRM system has three different 'sensors' on the bike (i.e., exclusive of HR):

1. the speed sensor;
2. the cadence sensor; and,
3. the power sensor.

The PowerMeter includes the cadence sensor and the power sensor in its housing, but speed requires a separate wireless transmitter, typically attached to the chainstay with zip-ties. The Duotap negates the requirement for the speed sensor, as it broadcasts speed data in ANT+.

In order to 'activate' the PowerMeter cadence sensor and, as Karsten mentioned, the reed switch for power, the PowerMeter requires a separate magnet positioned within the arc of the reed switch. Personally, I do not recommend using the stock SRM magnet for this purpose, as it is more intrusive than required. Instead, just glue a 1/2"x1/8" rare earth magnet to the chainstay/bottom bracket shell (depending where the reed switch is in relation to the frameset. If I recall, on the Madone, we put it high on the chainstay, as it was flatter there).