Responses from medium_grade

Best Tube Amp for High Sensitivity Speakers: 45, PX25, or 300B?
Personally, I love my Elekit 8600 300B amp. Even if you get someone to build it for you, the price is fantastic and you won't have to wait nearly as long as you will for a new Decware amp 🤮  
Is there a list of full-range speakers (20-20kHz) somewhere on the internet?
Try the Omega high output Alnico or 8 inch speakers. The speakers are configured to use a single full range driver and then a second identical driver cut off with a low pass filter around 200 HZ. I love these because you get the benefit of full ra... 
Made in USA
Omega Speakers are based in Connecticut and I know for a fact each one is handmade there.   
Cartridge burn-in
While I am a firm believer in "breaking in" most new gear, it is hard to quantify. It's hard to know how much of it is the gear itself changing character over time and your own ears becoming accustomed to what it's hearing and also not hearing. Th... 
100% USA designed & made DAC
Geshelli Labs. Just bought their J2 DAC for my office and it's absolutely fantastic for what they charge.  
I need help choosing a budget phono stage gift
Hagerman Bugle3. It's right in your price points and, because it uses socketed op amps, you can upgrade it later by swapping out the op-amps with discretes (Sparkos would probably work best).   
Which DACs are known to be sweet/rich/relaxed?
Try a Musical Paradise MP-D2, get the DAC chip upgrade, Jupiter Copper Foil caps, GZ34 rectifier and 6SN7 tubes. That ought to do the trick.  
Cornwall IV – tube (amp) choice
Have someone build you an Elekit TU-8600 (with Lundahl transformers). Best money you'll ever spend.  
Whats on your turntable tonight?
Return of the Living Dead Soundtrack  
Every day I see another turntable recommendation...
Hit up Kat at Upscale Audio. She's very knowledgeable and, if you buy the cartridge from them, they'll set everything up for you as well. 
2nd systems- who’s got one?
Four here: office, home office, living room and garage. Garage is my primary.  
American Made Audio Products
Omega Loudspeakers are assembled in the US with us made drivers. Highly underrated underrated.  
Usb or Optical
It depends on the quality of the USB controller. I've seen some devices (Raspberry Pi) where it seems to make a lot of difference. I always go optical or Spidf whenever possible.   
Please Recommend Highly Efficient Floor Standing Non-Horn Speaker Suggestions
Omega Loudspeakers. They're beautiful, efficient and sound fantastic.  
MM vs MC Cartridges
I echo Fuzztone. Get a step-up transformer from Your MC cart will get the authority it needs.