The 970 doesn't support upsampling the 990 does.
Also the 970 has analog bass management at 80 hertz if you have an SACD or DVD-Audio player without proper bass management (virtually all of them suck at this)
Interestingly the Cirrus chip supports MP3 decoding but the 1070/970 doesn't expose it. Probably a marketing decision on Outlaw's part (don't want to step on the 990's features too much).
Also in the pdf link it says it does DVD-Audio/SACD bass management (probably ADC/DAC work on the analog signal, yuck!).
Here is the link:
http://www.cirrus.com/en/products/pro/detail/P1031.html.