Do they have any difference at the pre-amplifier of audio output too?
What do you mean exceeds the specifications?
Ps: Are you a pilot?
Hi --
Not quite sure what you mean by "pre-amplifier of the audio output." The Yamaha YDA164C has an integrated DAC. It receives a serial digital audio stream from the tone generator integrated circuit (IC). It's all digital right up to the YDA164C.
WRT the specifications, I may have misled you (and me, too.
) After looking at the data sheet for the YDA164C, the amp is 20Wx2 "Maximum Instantaneous Output" and 15Wx2 "Maximum Continuous Output" into a 4 ohm load (i.e., a 4 ohm speaker). This is the old "peak vs. continuous" rating disparity. The spec in the Owner's Manual probably refers to "Maximum Continuous Output".
I don't know enough about the analog design to say if the S970 digital amps are further throttled back to 15W continuous for both tweeters and woofers, or if the design is 15W plus 15W per channel due to bi-amplification.
Whether the S970 actually sounds better than the S770 to the ear, I couldn't say because I haven't A/B tested them.
Hope this helps -- pj
P.S. Pilot? No. Just a grandparent whose grandson lives far away.