There are various ways for linking repeaters. Here in the Mountain West there are a several different networks of repeaters. The big ones I monitor are the Intermountain Intertie (http://utahvhfs.org/snowlink.html
) and Cactus Intertie (http://www.cactus-intertie.org/
) which is the largest linked repeater system in the world, covering most of the Southwestern US and the Washington DC area. Some are private and some are not always linked (but typically can be interlinked on demand).
Your local club will have information on linked repeaters in your area.
Any standard radio that can connect to a repeater is capable of connecting to linked repeaters. Nothing special is needed. The VX-8DR is WAY more than capable of doing this. There's no such thing as an IRLP-enabled radio. IRLP repeaters function pretty much like any other repeater, except that they use the internet to communicate between repeaters rather than over-the-air signals. If you want to reach out to other parts of the world, IRLP is a fun way to get started. Again, your local club will have info on IRLP access points, permissions, etc.
APRS is something else entirely and doesn't really fit into this discussion. It's generally for local sharing of position and other data.
To be a bit blunt, if there's not much traffic on the local repeaters, you could always try talking on them a bit more. :-)