Glad to hear you're making progress!
Your skill with the tool will improve over time as you experiment with different settings. A quick start method is included in the guide and also here:
viewtopic.php?f=8&t=221Also careful listening to stereo source material with headphones will help you to understand what is possible with a particular source, considering that spec spreads the original stereo mix over 5.1 channels.
Having said that, it is however possible to move things around by either re-wiring the output of spec or changing the pan settings in Zpan. I've seen this done by users, for example, in early Beatles tunes where a vocal was ONLY in one stereo channel and thus in only one of the surround speakers after spec. Swapping the surround channel for C made a mix that was more "modern", with the main vocal in the center channel.
Re: background vocals, if they were mixed mostly or "hard" left and right in the stereo then they will come out in the surrounds in spec. If they were mixed close to center (but not dead center) you can pull them into left and right with the arctan width settings, or into surrounds with the arctan "diagonal" settings.
Adding ambiance is technically possible but gets into our philosophy of conversion or "upmixing". What we are doing with spec is NOT creating a surround soundfiled as if you were sitting in the audience of a reverberant concert all with the stereo mix coming from the stage. If that's what you're looking for chances are your home theater receiver has some DSP setting that will do that for you.
What spec does do is put you onstage with the stereo mix/band members around you. We think this is more aurally "exciting", true to the original material, and just sounds better than muddying things up with added reverb, etc. There is a "wow factor", that happens when each instrument comes at you from it's own direction, vs. from the same direction as other sounds in the mix. By spreading out a stereo mix into 5.1 channels (Slice) or into a 360 sound field (ArcTan) Spec can achieve this effect (depending on the original stereo mix).
But, to each his own, so if you want to add ambiance in the rears you can always insert a VST in the rear channels, and/or use a mastering VST that adds ambiance. If the VST has any processing delay you'll probably want some help getting it into the layout and keeping everything is sync.
FYI, overtime we've seen a normal progression with new users where they start out wanting to add lots of things to the process. Mastering VSTs, ambiance, aural exciters, etc. However, over time they generally come to a "less is more" conclusion and go back to the bare bones spec layout, perhaps with more practiced skill in the settings.
We're here to help you on your journey.
Good luck,
Z