[octatonic]

I'm running a HD3 system- but if I was buying now I would buy:

Logic Pro $1000
RME Madi card $1300
SSL XLogic Alpha Link Madi converter. $3500

This would give you 24 analog IO, 24 digital IO.

Otherwise I'd look at the Aurora 8 or 16 converters.
You could either use a Lynx audio card or their firewire card.

Or an SSL Mixpander

Or an RME Fireface

Or an M-audio Lighbridge (which would allow you to switch between PT M-powered and Logic).

There are loads of options that would work for you.