In my opinion the better sounding choirs of the type you require can be created using Logic's software instruments.
However, this would require you to either use a MIDI keyboard to input the notes to Logic or draw/add them in using one of Logic's various MIDI editors, probably the Piano Roll... or Matrix Editor as it was called before Apple removed some of it's quirky coolness.
After choosing a software instrument patch that suits your needs a part could be played or drawn in and then bounced to a standard audio file. Sounds like a lot of work but it's relatively easy, you've obviously got the computer chops to do it.
1. Open Logic, create a few instrument tracks, chose one:
2. On the Far left you will see two channel strips, the one furthest left is the Instrument channel strip, the other one is the Master Output bus, it will be common to all of the audio/instrument tracks.
3. At the top of the far left channel strip is a drop down labeled "Setting", click and hold on it.
4. Scroll down, you should see Texture and Choir menu headers, choose one, if you have a MIDI keyboard hooked up you should be able to hear it by playing the keyboard, if not, you will have to use the Pencil Tool to add a MIDI region on the track.. then, double click the MIDI region and the Piano Roll editor will open and you can mouse on the visible keyboard to get an idea of the choir sound.
A nice selection of notes from low to high might be: C G C D Bb (B-flat) the first note starting fairly low. Then mix in an Eb or Ab.
To be honest there may be loops that do what you wand/need but I don't use the prefab stuff because I usually have more specific needs, however, there's a few folks here that do magical things with loops and could probably help you out.
