Read most of this thread over the course of a week, but still confused as a non technical person who enjoys home theater and 4 channel stereo listening through my home theater system every now and then. Do these lower SINAD scores affect sound quality in DIRAC mode? Only if using the internal amps? I couldn't find a clear answer in the 80 pages of this thread. I run all outboard amps and was looking to upgrade to the 3800 and turn off the internal amps for the supposedly cleaner signal/better sonic performance of this feature.
SINAD ... threshold of audibility is circa 60db ... anything with SINAD over 70db is not going to have any SINAD issues
Dirac is a completely seperate issue - to do with Room and Speaker EQ.
Denon & Marantz purchased exclusive licencing to Audyssey Room/SpeakerEQ about 10 years ago - which is why after 2014, you don't find Audyssey in any non D&M components. - Dirac and Audyssey do much the same thing - however Audyssey basically stopped development after selling to D&M, whereas Dirac has been continuing its development and improvement - the end result is that Dirac tends to be better (note "tends" - in many many cases, there is little to differentiate between them!).
However D&M clearly felt threatened by the growing reputation of Dirac - enough so, to provide a future Dirac upgrade option...
With the optional apps for Audyssey, and some time and effort, an Audyssey based setup should be just as good as a Dirac one. (Dirac is probably easier to get optimal results with)
Internal vs external amps - the X3800 doesn't "turn off" the internal amps - but if there is no load on them, then there is better stability of the power supply, and that results in a better/stronger signal on the preamp outputs - specifically, it can drive beyond 3.5V in that case without increased distortion, whereas when running speakers with the internal amps, the output can be limited to around 1.4V (before distortion kicks in).
Is this a problem - well that depends on your external amps!!! - My external amps produce max rated power at a 1.4V input level.... so for such amps, it would not matter whether the internal amps are in use or not!
If your external amps require a higher voltage input (low gain amps have become a bit of a thing in some Class D designs) - then this might be an issue - it is worth checking what the amps input requirements are!
Best case in terms of sound and value for money (IMO) is to use the internal amps for surround/height and external amsp for the heavy lifting of the front L/C/R - make sure the external amps can work with a max (continuous/rms) level of 1.4V - and that way you get the best of both worlds.
This, of course, assumes that there is something to be gained from external amps - which is NOT universally true - if your speakers are high efficiency 8 ohm speakers - you are unlikely to get any benefit from external amps - it is only where they are low efficiency and/or low impedance, that the capabilities of the internal amps are placed under sufficient stress, that the sound is impacted, and external amps can provide a performance gain.
My speakers are relatively low efficiency (86db/wm) and also low impedance (4 ohm nominal, but with drops down to 1.6ohm) - most AVR's don't do well with them as a result.... external amps are the best solution. (but I still use the internal amps for surround)
If you already have all outboard amps, then all of this is red herring central - unless your amps require more than 3.5V for max rated power.
What are the amps? what are their ratings?
