If you are willing to wait, you could get the Logitech Z333 Multimedia Speakers. As this hasn't been released yet, I can only go off of the spec sheet and online reviews, but this looks like it would fit your needs.
This is a 2.1 speaker system that costs $80 USD. The subwoofer is flat-bottomed, has its own independent controller, and has a 5 inch, front ...
I recently had the same problem and in the end went for the Soundsticks III from Harman Kardon. They look and sound beautiful. Sub is on feet though, but gives a really tight sound.
I got mine for €100 (around $120).
It has the following features:
Price around €99 (at least here in holland)
Subwoofer with: independent control, 20+ Watts, 6 ...
This one looks like it meets your requirements in terms of size and dialog volume: https://www.bose.com/en_us/products/speakers/home_theater/bose-solo-5-tv-sound-system.html
Has mounting brackets
Has "Dialogue mode to hear each word and detail clearly"
Has Optical audio input (digital)
Is < 30" (21.6")
You want a "Sound Mixer". If you are working with analog audio signals, there are several options: Here is a cheap one that has 4 inputs and here is a battery powered option with better quality that has 2 inputs.
Unfortunately there are not any devices that share a USB connection between multiple hosts. That is just a limitation of USB. USB was ...
I was looking for ways to control the voltage of an outlet, since we are in quarantine, I would not find resistors and transistors. But I just remembered that USB cables already do this job for me. As I have several unused at home, I stripped one, stuck the negative and positive of those that were connected to the battery and it is working perfectly. I was ...
Standalone pitch adjuster devices like the TC_Helicon which can adjust pitch to the accuracy you specify are studio devices, designed to fit into a 19" rack mount frame. You'd need to interface them between the audio source and your amplifier, if your amplifier supports that. They will all be more expensive than used PC running tone adjustment apps.
8 ohms is nothing, you don't need an amplifier for that. The power supplied with a mobile phone is enough to drive your headphones. You'll blow out your eardrums with an amp. (250 ohm headphones and I'd recommend an amp, but you could still get away without using one at that level)
If you still insist on getting an amplifier for your headphones, you can get ...
How about something like this? Sony HT-XT3
This is actually a soundbase, which sits under the TV....but it does fit the rest of the specs as far as width....Finding a match for your specifications, is being tedious lol.
Here is a review if it helps
As far as HDMI pass-thru receivers, yes they are on the market.
I am currently using a Denon AVR-1513 to route output from my PC/Xbox One, to my HDTV via HDMI. This specific unit has 3 input with one output as far as HDMI goes, along with the usual optical/coaxial/RCA/ outputs you would expect.
Mine is a bit lower end so it only has pin connectors ...