With Yamaha receivers they do the following:
Straight mode: signal is unprocessed from source but crossover is active thus you have sub working. Also video through the HDMI works as well.
Pure Direct: Signal is unprocessed, HDMI video is turned off, all amplification except for the fronts is turned off.
So basically you have two options:
If you are using an SACD player through HDMI, in straight mode you can do multichannel SACD. Considering the DAC on your receiver is DSD discrete if you have a compatible player this is the way to go.
If you are doing 2ch SACD you can do pure direct except you can only get 2ch.
Straight is the same as Pure Direct except you can do 5.1, and video will work through the HDMI. Now there is also Stereo mode which will work the same as straight mode in 2ch except you can use EQ.
Straight mode - up to 7.1, crossover active, no EQ, full HDMI function
Pure Direct - 2ch, crossover inactive, only FL/FR amps on, no EQ, HDMI off
Stereo - 2.1, only FL/FR amps on, crossover active, EQ, full HDMI function