Best path to upgrade from PTHD on PowerMac G5?

[el biciclista]

Please help with some advice. I am not up on the best options for upgrading my system.

Here is my system:
- PowerMac G5 Dual 2.7 running OS 10.5.8
- HD2 system with PCI-X core card and 2 process cards
- PT Version 8.0.1
- Two 192 Digital I/O units connected to Lavry converters.

I have been postponing upgrading from my trusty G5, but my hand is being forced.........for example:
- I want to buy the virtual instrument Strike.......the system requirements include "Intel-based Mac".
- I want to buy an Axiom 49 keyboard..........the system requirements include "Intel Core Duo".

Some questions:
(1) Since I mix out-of-the-box and use almost no plug-ins (iZotope 4 and a few virtual instruments), is the Mac Pro Quad Core sufficient?
(2) Is it time to go completely native w/o an HD core card? (It would be pretty strange w/o HD ). Would this be adequate for me?
(3) Are my 3 HD PCI-X cards worthless, or can I upgrade from them to a newer Core card, if I continue to stay HD (versus native)?
(4) I have 18 digital Out's and 4 digital In's (I convert with Lavry converters). If I buy a new HD card, then I assume I would continue to keep the two 192 Digital I/O's. Alternatively, if I go native with no HD card, how would I get the digital signals in/out? Can I buy a 3rd party I/O card for this?

As I said, I haven't closely followed Avid changes, so I am trying to sort through my options.
Any help would be greatly appreciated!