Hi Geoff,
Xpression is sending over a 32 Bit TGA so we still need to load the Alpha into a second Media Store channel so that you can have the Key channel. A Self Key is doing a LUMA key so you are applying clip and gain to the Luma channel of the video image -- not the same thing as a linear key.
You do have 4 channels of media store when you are in Dual/Swish/Swish+ modes. All modes are standard with the system. In Tall Mode you have 2 channels but they have access to all 4 GB of RAM. Note that the RAM is 2 separate SODIMMS so it's not that you have 2 channels but rather a 1a and 1b, a 2a and 2b as to span the ram you swap the readout channels on the fly as the system moves from one DDR to the other.
Swish modes is used to "dedicate/lock" Media 2/4 (V/A) to the Transition area to only be used as a Media Wipe. Swish+ allows the user to select it in the Media Wipe and any bus on the switcher at the same time. So in theory you could have Channel 2 on air in a Key or BKGD and then select Media Wipe press your Wipe selection and "load" the channel on air by mistake. However we did not want to have a mode that did not allow the user to not have the option to use it how they liked.
#CrossOver