Tascam released v2.00 drivers and v2.00 firmware updates for all 4 interfaces, the 2x2/4x4 and 16x08 on 9 November and the 20x20 yesterday.
 
16x08 http://tascam.com/product/us-16x08/downloads/
20x20 http://tascam.com/product/us-20x20/downloads/
 
2x2 http://tascam.com/product/us-2x2/downloads/
4x4 http://tascam.com/product/us-4x4/downloads/
 

Thanks.  I just checked Monday  :)

They added a 'mixing driver' mode that allows simultaneous ASIO and WDM. Will have to check that out. They do note that using the new mode will increase latency a bit. While not ASIO multi-client, it may be possible to have Windows use WDM and SONAR ASIO.

Another note:
 
After installing the new driver, check your Windows Playback devices and Recording devices defaults. Mine had been changed to the new Mixing Driver (WDM). For the time being, I reset them to the internal Realtek audio devices.

My defaults didn't change (8.1)

Yet another note:
 
Woohoo! For those of you with the latest Kontakt v5.6 who got no audio from the standalone version with the ASIO driver and were forced to select the WASAPI driver...great news! A new driver shows up in the Kontakt Options dropdown: "US-16x08 Mixing Driver" in addition to "US-16x08 ASIO".
 
I can now get audio from the standalone Kontakt from my mains, and not have to use the internal Realtek audio.
 
Note that Kontakt reported an increase in latency from 10.x mS to 16.x mS. That's not an issue for me since I use it mostly as a previewer, but might be for some.

Good info.  Thanks.

Just wondering, if you record with midi keyboard and soft synth, what would be the round trip latency for Tascam interface ?