Schiit Freya+(Plus)

Thanks for the report. Never tried the Silvanias myself as there were tales of excessive brightness and impedance troubles. But you never know until you try, and it's not that expensive. Plainly you're right about build quality. My own approach has been to get along with the Freya, which is fun and easy, while upgrading other components, cables, conditioner, then finally decide on my "forever" tube pre. So far, so good, and I'm due for another roll now that the sound of newer gear is stabilizing after burn-in. 

I have question about buying XLR cables. I went to Amazon and found the Amazon Basics XLR microphone cable for $7.99 each. Are those cables any good?

https://www.amazon.com/AmazonBasics-Male-Female-Microphone-Cable/dp/B01JNLTTKS/ref=sr_1_1?crid=17E0V6PZJT9KL&keywords=xlr+cable&qid=1641006691&refinements=p_72%3A1248939011&rnid=1248937011&s=musical-instruments&sprefix=xlr+cable%2Caps%2C195&sr=1-1

Another question about XLR cable vs RCA cable. Does it sound any better if I use XLR cable? I have never use XLR cables before and XLR cables seem to be very popular for everyone.

IMO, you will not be satisfied with super-cheap XLR interconnects in a high fidelity sound system. At least not if you compare them to much higher grade gear made by Audioquest, Pangea, or a great many others specializing in audio playback. You can easily get much higher quality without breaking the bank. For example, 

AudioQuest Red River XLR to XLR Analog Audio Interconnect Cables - 3.28' (1m) - Pair is a good high-end entry level choice.

Now, whether XLR is "better" than RCA, there are no absolute rules. XLR (balanced) does have certain advantages such as higher gain, as well as theoretical advantages. I am running fully balanced from source components to Freya+ to power amps, but not everyone does this and it is hardly necessary. Decent quality RCA cables are generally less costly than XLR, for obvious reasons.

Is there a way to tell if you bought bad tubes when you put them in the Freya? I mean, what if one of the tubes is not working, will the Freya let you know if one of the tubes is a bad tube?

You can email Schiit directly on their website contact link. I had a bad tube and was told to reverse the two tube pairs. I did so, and the fault was corrected. A bad tube on one side may not sound bad on the other side.

Of course, since then I have rolled in other tubes and not had a repeat, but it is surely only a matter of time before this recurs. When it does, I will start by reversing the tube pair to see if the problem clears up.