.....Budget not really too much of an issue. Just want best sound possible
Oh man do I love it when people say that!!!!
Yes, almost any modern laptop will do the job. But the soundcards that the factory uses.... a chip on the MOBO in most cases does NOT do the job.
Purchase a USB based external musical interface from Focusrite, M-Audio, Presonus, Roland, or other, which supports the number of outputs and inputs you need. For backing tracks in a church setting, a stereo rig is sufficient in most cases. 2 ins, 2 or more outs.
Some interfaces have the MIDI (5 pin din) input on them as mine does, and some do not. New midi devices have started using USP ports. So, be aware of your needs in that respect. Look for that midi port on the interface, it makes it easier IMHO. However, direct midi input to the computer via USB also works. Just depends on how you want to do it.
Be sure it has NATIVE ASIO drivers.... in other words ASIO and not some driver wrapper or proprietary codec.
Other features you may want include nice built-in preamps on the audio in's, phantom power, more channels, DSP processing internally, etc.... if you plan to use it to record.
I find that BB tends to run well on my off the shelf (old Inspiron) with the MME driver and running BiaB without issues. I use TTS as my default synth. It's when I open that same project in Real Band (RB) and try to play it....if it has any synth tracks in it, I end up with huge latency issues.
I can then take the very same project, on this same computer, and reopen it and play it with my Focusrite Saffire interface connected and there is ZERO noticeable latency.... everything plays in synch.
So, a decent interface, running ASIO, does make all the difference in the world. Just run the interface's stereo outputs to the PA board and let it play.
Expect to pay around $200 (+/-) for a nice stereo interface.
Hope this helps you a bit.