ASIO 2 has been out for years. I would guess most vendors are using the ASIO 2 SDK as it offers 64bit support. There is still a "one driver at a time" host restriction. It is possible to aggregate devices, some manufacturers provide such a driver.
 

Herb - there's nothing to download for ASIO 2 unless you're talking about the SDK (which I referenced above) or ASIO4ALL.
 
the only reason I mentioned downloading the ASIO 2.3 SDK is so that if one is curious about reading the ASIO Specification they could find it in the SDK.
 
SDK is not necessary to be downloaded by anyone except developers (SDK stands for Software Development Kit).
 
there is now and always has been a "one driver at a time" restriction for the ASIO spec.
 
I'll show you a screen shot of what Sonar/MC does when it sees 2 ASIO drivers if you want, but bottom line is that you can only CHECK one of them.  if I have 2 devices connected to my PC which use ASIO drivers (which I often do with my MOTU and my yamaha keyboard) - sonar will only allow me to use one of them and the other is grayed out.

Here is another link that may prove useful.
 
https://www.steinberg.net...opic.php?f=34&t=48