I'm in the same situation. Been doing colour separations for T-shirts for over 25 years. So have downloaded APhoto and ADesigner to test and see if they compete with PS and AI combo.
With few clicks things are not looking good. I see there is no support for Multichannel PSD files. APhoto can't open them. I use these for full colour Simulated Process separations. They contain many halftone spot channels, sometimes up to 12-15 cols. If I covert the multichannel doc to greyscale or CMYK, it will open in A Photo, and the extra separation channels are visible in the channels palette. However I cant click or view them, all I can seem to do it delete them? Not much use. In photoshop I can access these channels and work on them with curves and all the other tools in the tool box. Then output.
The above processes are not just for DIY T-shirt print shops. This is how the whole garment print industry works around the world. From the small to the huge factories . -Unless they are using DTG printing-.
Apparel Screen printing is a massive global industry.
The above issue would also affect the whole off the offset CMYK print industry as their seems to be no support for Bump plates to add to a CMYK separation. ? or is there ?
Noted on the comments to use layers instead of channels. But this would be a nightmare for output. You would need to output each layer on it own for all colours. ?
Ive tried to attached a screen shot of an example but the upload fails every time sorry.