Responses from nordicnorm

Options for $1k or less DAC?
Lots of choices in the under $1,000 used marketplace.Schitt, Denafrips, Chord, Ayre, LKS,... take your pick. All are solid performers.It all depends on how it integrates with the rest of your chain and if you like the result. 
Speaker upgrade for classical music
I play trumpet in an orchestra (although I sometimes slum in Big Bands 😎🎺).The speakers that I have are Martin Logan Spires. They deliver what you are looking for.I power them with either solid state or tube monoblocks.My s/s monoblocks are Soundc... 
HDMI (i2s) recommendations for Denafrips Gaia -> Terminator
For I2S, length of the cable is the most critical performance factor. You want to go very short e.g., no more than 6 inches.Sure, a longer cable will work, but the I2S standard was designed to communicate PCM audio data between integrated circuits... 
DAC's Made in the USA
While I am only in my 60’s, I fret over the same auditory limitations as you (hopefully I’ll make it to my 80’s).I would recommend that you get an auditory test to see (objectively) what frequencies you can hear. Buying equipment that can resolve ... 
Speaker recommendation $10-20K (with some requirements!)
Merry Christmas!What you're looking for you can find in hybrid electrostatics.I'm partial Martin Logan myself. Audition a pair of ESL 11A's If the bass doesn't grab you, add a sub.As ... 
How old are you?
62... but still act 18 (according to my wife). 
Phono Preamp suggestions $2000 (pre-rabbit hole tire kicking edition)
For MM, I’d recommend the Croft Acoustics RIAA Phono Stage. It sells for under $1,000 (£500). Highly underrated.Tubes: 2 x ECC83 Sensitivity: 2 mV for 0.5 V rms Input impedance: 47 kΩIt's magical with my London Decca Super Gold cart. 
Recommendations for fast sounding cables
Teo Audio Game Changer ICs have a money-back guarantee so you have nothing to lose (except postage). 
Speaker upgrade
Have a listen to the Martin Logan CLX Art or Renaissance ESL 15. You might be pleasantly surprised  - they do exceedingly well on the type of music you listen to (except rock).As a musician, they are the closest I've heard to having the instrument... 
Streaming DSD to DAC options on home network
I use a dedicated small form-factor pc (Asus VivoPC) that is fan-less. My digital files are on an external SSD. This is connected to a DDC via USB then to my DAC via I2S (then on to my preamp).I used to run it headless (no monitor). I would remote... 
Nice choice! Enjoy! 
Best 2channel amps for my speakers.
You haven't mentioned a budget but those speakers scream out for TUBES!! 
From another Audiogon post:" Compared with and 8 ohm speaker, a 16 ohm speaker requires that the amplifier put out twice the VOLTS for a given power, because it draws half the amps [amperage]. Solid state amps are limited by the volts they can ou... 
What speaker – under $10k – has the best timbre and tonal qualities?
In terms of accuracy of timbre, the speakers under $10K who deliver (that I’ve listened to) are:- Martin Logan (Spires, Montis)- Yamaha NS-1000(M)- Tannoy WestminsterAs a musician, that has always been my number one expectation of my audio system.... 
Do chinese tube preamp/amp clones interest you?
I bought a Chinese tube amp (Music Angel XD-800 MkIII) about 12 years ago just to play around with upgrading it. IIRC, it was around $500.When I received it, I opened it up. It looked like the tech who assembled it, just put in whatever parts he h...