Logic Studio apps Mainstage live with MacBookPro built-in audio?

I'm bouncing away in L9 on my home iMac creating a setlist of songs made up of backing stems to playback live in a MS 8 track mixer. I'm using an 8 in/out FW interface.

I have in plan to get a MacBook Pro just to run Mainstage playbacks of the above stems (I'm not planning (well, at this stage anyway) to use any of the live effects or instruments - just to run stereo playbacks to the band IEMs and to the PA).

I was thinking I'd have to get a 2 channel audio interface to do this then thought, hmmm... I wonder if the MB pro on-board audio is up to this? (I'm all for a simple life)

Any opinions please? I'm new to Macs so pls excuse this basic question :redface:
What else do you want to do, apart from playing audio files?

Very little Peter - I use a hardware pedal board for my guitar effects. I'm just looking to have a virtual MS backing band whose groups of tracks I can have playing or muted depending upon who is playing in the band that day. (It's a church praise band and sometimes the bass or keys or drummer doesn't show). I want a click in the band in-ears and the un-muted tracks (probably a max of 6 stereo playbacks of 3-4min songs) going to both iems and PA.

Although I use Logic s/w instruments a lot during the Logic arrange phase, the results are bounced down (by group - guitars, keys, backing vocals etc) to seperate AIFF files for import into MS configured as an 8 track mixer.

I want to set up setlists (usually only 6 songs per service) that I can step through.
Nice idea, this playback depending on available band members :) But it doesn't sound like a job for Mainstage. Why not sparing the extra work and stay in Logic? You could have the stems of the instruments in one project and simply start/stop the playback. Unneeded tracks would simply be muted.

You would need four transport buttons on the controller:
Go to next marker - Do this before you start a song.
Play - Play the song.
Stop - Mhm, what for is that? Ah yes. Stop the song.
And just in case you accidently step on the wrong button: Go to previous marker.

Each song would have a bright marker to show you where you are. With an open marker track and a proper zoom level (only one colour on screen) this is easily visible from several meters. Preferably you play only audio files without effects, so the system would be almost 100% reliable, assuming your computer is ok.

Here is how it looks when the background choir and the
bass didn't show up. Each song has a coloured marker:

Just to reiterate what Peter is saying - staying in Logic with audio files only is the best way to go.

My band uses Logic live on the gig - for backing tracks - and opening/closing audio only projects is almost instantaneous when there are no instruments or effects to load.
Regarding the built-in audio interface, yes you can use it although it is not the best quality. A small USB or Firewire interface would be better. In any case, make sure that all cables are secured. Stumbling over cables and pulling the plugs out is very dangerous for computers on stage. Such an accident may kill Firewire ports or ruin the computers audio jacks, which are very weak.

An audio interface with at least 4 outputs would also solve the routing. One pair to the PA, one pair to the in-ears. The setup can grow, later you may want a small mixer with good audio quality and a 31-band EQ to adapt the sound to the room.
Hmm. Food for thought chaps. Thanks.
I must say I'm hung over from my Logic 5.5 (yes 5.5!) experiences - I was still using this as my main tool until 2months ago! Just one song was pushing things :) so I was thinking MS with everything loaded in RAM might be a good thing.

Thinking about the audio, I probably need an interface anyway as I'd like stereo to the PA and a click as well. I have a couple of (Behringer but they sound pretty good for the $$s) usb interfaces. Is it possible to use both on board and usb interfaces at the same time? I guess I could try this.

I need to look about for some interfaces anyway - the Gio seems popular but I'm not sure if it woud be a good fit for me as I don't use the effects / instruments live.
Point noted about the cables - I already have the usb cable tie wrapped to a HD music stand the (Windows) PC laptop sits on.
Is it possible to use both on board and usb interfaces at the same time?
Yes, on the Mac this is called "Aggregate Device". You find the editor in the menu of the "Audio/Midi Setup" application. The idea is to combine multiple interfaces to one bigger, virtual interface. In your audio applications you select this virtual interface and get the inputs and outputs of all physical interfaces like it were one hardware box.

But honestly, I would not do it in this case. Take a rugged interface with enough outputs, preferably rack-mountable. There are mobile racks on the market that accommodate a couple of 19" units and a case for the laptop. For some small combined Audio/Midi interfaces you can get brackets to mount them in a rack. Or you screw the box to a 1 HU rack shelf. A compact case, just a few cables dangling around and a clean software setup is always best on stage.