Still trying to get a grip on that. Soundirok recognized my existing playlists (created with MPad) and they work fine, plus you can edit the playlist. I think Soundirok may use collections as playlists, but I'm not sure about it. If you press on a single song a menu comes up and there is an option to add it to a "collection", just haven't had time to mess with that function.
I am still creating my playlists on my Mac (using Vox) and then I use TextEdit to mass-change the leading paths for songs to match the mount point of the music folder on the Bryston BDP-1. You can SMB-mount the USERS share and directly copy/edit the playlists and then just Update - BUT, if you do that on a Mac, be sure to run something like "BlueHarvest" (Mac app) to prevent metadata files/folders from being created in the BDP, which will show up as extra playlists with goofy names.
And, as you've noticed, you can edit existing playlists via the Soundirok interface, but I haven't seen if you can create a new playlist from an existing playback queue on Soundirok. I'm either missing something or that's sort of the last missing feature for me.
As for "Collections", you can create device-local playlists that are on your iPad with Soundirok. I haven't used this, but I have used the "Intelligent Sets" feature, which lets you define "Smart Playlists" for MPD which works across multiple devices (anything that uses MPD for playback). This feature is very cool and I've had created a number of sets, based on Genre and Artist parameters.