You asked about tweaks
This is what I have going on. Right now my first 950 (the hissier one) is in my rack. AND it has LESS hiss than it did. If I tweaked pertinent to the reduction I have experinced I’m at a loss how to tell you to duplicate. Realize that this was MY first hands on foray into AV. By that statement I mean….I’ve been listening to sound all my life. Music is a necessity in the background of my days. The 950 purchase, (and shortly before) was the first time in my life, I began to pay attention to how to set up a AV system, and why different setups (brands/models/config menus) affect the ‘quality’ of the sound.

Since the 950’s arrival, I have learned to move speaker terminations/route interconnects/calibrate and navigate system setup menus. Source/inputs/SPL/Distance/crossovers/tone controls (treble/bass)/SP modes. The whole side of AV that I left to the ‘men’ till now.

I have changed and played with settings in so many different configurations that there is no way I’d be able to draw a ‘backtrack’ map. Many of these settings were changed over the last months due to advice that was given directly and/or reading posts and contemplating for myself what to attempt and after some critical beginner’s mistakes. (Which most here, with much experience would have skipped over entirely) Ex: Boosting my surrounds way out of proportion, in my excitement over playing with DTS and DD 3.2/1.

If any of the above had an effect on hiss, you explain it me? I know that I (as anyone who loves and listens with heightened attention to all music reproduction) had had opinions on the ability of any system to reproduce it. This setup sounds simply good/better/best/excellent. I never contemplated upon the many variables, which can effect any systems output. Which brands more ably pass the sound and how to tweak any given system to its fullest potential.

When I mentioned I was not happy with the 950 the first weeks, this feeling was not centered on the subject of hiss, but on the general experience of the sound in total. My husband, (who has not become involved due to his own major project at the time) and I both found the 950 fairly flat and unappealing out of the box. (But I set the menus) To be honest I was happier with the output of my old Pro-Logic Receiver. As I learned to navigate through calibration/distances/crossovers and brought these parameters in line with what was best matched with my speakers, each step forward, was as if I had unboxed a new unit. Every other foray into setup, the sound improved dramatically. Could any of this affect the level of my hiss? I don’t’ know, if I had more experience in setting up a system, I could more easily tell you, I changed this and it did that, since I would have been familiar with a baseline average setup and more quickly moved forward from that starting point. As it was, I used up many days, (what’s a interconnect?) learning the bare bones basics. I don’t know what all I’ve done as I’ve reset the system countless times.

Burn in. A subject that can be debated hotly both sides by some engineers. (Whether or not it occurs and can effect sound) In my experience it does occur to a ‘degree’ in systems. But then I have also proved to myself that a change in interconnects does have a net (positive or negative) affect on the quality of sound and picture. I came to this opinion by changing brands out with absolutely no other adjustments made concurrently to the system, and will beg to differ with any (many) who state it does not. While I understand the tricks the brain can play with ears. Changing my component cables alone between 3 brands visually affected color scale on the display to a dramatic degree.

Leading to my contemplating whether there is a possibility that the 950’s burn-in has reduced its hiss over time.
How much effect I had on the distance out I was able to hear hiss by system configuration and how much is due to burn-in, I cannot judge. I could hear ‘hiss’ out to my seating. When the 950 first arrived. Hiss is NOT audible at seating under any source at this time (I have to go put my ear near speaker to find it now) this reduction occurred BEFORE last week’s speaker upgrade.

It crossed my mind when I installed the Beethoven’s that I would most likely increase the distance out of audible hiss than the distance heard with the less capable Def Techs. Counter to my expectations, Hiss has been reduced AGAIN.
I could hear hiss out approx. a foot on the Def Tech center just before the speaker upgrade. The hiss is closer to the fabric with the Vienna Acoustics.!?!

I will say this. When my hiss was audible to seating (to me) on certain passages played on certain sources, I had already made the decision to keep the 950 regardless. After comparisons to everything that I could request or heard playing at any electronic store I have frequented in the last months. Hiss or no, the 950 in totality beat the competition.