|ASDL or DSL. ASDL is a router and modem rolled into one, like the Netgear Rangemax. a DSL router is just a router and is compatible with DSL lines (virgin,BT etc).|
I think you are getting a bit confused there Gareth. ADSL stands for Asynchronous Digital subscriber Lines to differentiate it from SDSL which stands for Synchronous Digital Subscriber Line. DSL is just a collective name for both that does not differentiate between ADSL and SDSL.
The difference between ADSL and SDSL is that ADSL has a high downstream bandwidth and a lower upstream bandwidth. SDSL has the same bandwidth in both directions.
If you are using SDSL you will need a modem/router that can handle SDSL. Most modem/routers sold for the home markets are ADSL as SDSL is a lot more expensive and is usually only used by business.
A router without a Modem will work with ADSL, SDSL or cable even as the WAN input will just be an RJ45 Ethernet connection coming from the appropriate Modem. Its the Modem that does all the work. A router is little more than complicated junction box.