Protools only works with Digidesign hardware and some M Audio units.
You get Protools HD which is “proper” Protools and if you’re on a budget you can forget about that; really expensive stuff.
Or there’s Protools LE which works with the MBox and Digi systems but even by prosumer standards these are pretty pricey and you’d have to go for the top models to get near the number of mic inputs that you need. (I don’t think any of the MBoxes have more than 2 mic ins, the Digi 003 rack has 4 mic ins and will set you back about $1,000, just to give you an idea). Of course you can always buy additional mic pres and use the line ins on the interface but that drives your costs up.
So I reckon your best option is Protools “M-Powered”, i.e. an M-Audio interface that runs Protools. The Profire 2626 will give you 8 mic ins and can run Pro Tools for around $700 (that’s assuming you have firewire)? You generally tend to get 2, 4 or 8 inputs (and then going up in multiples of 4) so getting something with 6 inputs is probably not likely. It’s always good to have a couple more than you think you’ll need anyway.
Of course your options are much greater if you’re not tied to PT but if that’s what you want/need then broadly speaking those are your options.