MME, WDM and WASAPI are Windows drivers. If you select any of these types your audio is passed to the OS which then hands it on to the interface. This is equivalent to Core Audio on the mac, except that Core Audio allows lower latencies than MME or WDM (not sure about WASAPI: I gather this is much better but I've not tried to use it for audio production)

ASIO works differently as it allows the DAW to commmunicate directly with the interface, without the OS as intermediary. This can give excellent low latency performance (if the ASIO drivers are written well) but it also explains why they tend not to be multi-client: the idea is that the DAW completely takes over the interface, which means only one app at a time.

ASIO is still the standard on Windows for audio production, so I would suggest trying to solve your ASIO driver issues before resorting to a different type. Have you checked you have the latest version of the driver installed?

Also you say that swicthing drivers to MME and back to ASIO cures the latency problem, is that correct? Have you tried just changing ASIO buffer size instead? What buffer size do you normally run?

MME sure runs really fast but I can't do VSTi monitoring.

Really? Software monitoring through your DAW should work the same regardless of the driver used, except I would expect much higher latencies from MME than from ASIO.

Thank you for that excellent explanation.
I'm using the latest driver and this happens at any buffer setting. It happens once I hit a certain track count.