Could use some help with a tough match

Well Threshold is right, you will not have close to a 10X ratio. You have a 183X ratio (75000/410). What they didn't tell you is that 10X is the MINIMUM recommended ratio. The higher the better. 183 is much better than 10, so no worries.
Obviously BAT gear was designed to run balanced. You can run it unbalanced, but you will not get optimum performance. This has nothing to do with the impedance matching though.

Cheers,
John

John,
If I understand the conversation correctly with Threshold if I installed balanced inputs it is not a matter of straight math. The input impedence of the Threshold's would be approximately 600 ohms balanced. That was the issue. Certainly not an engineer but that's the feedback I received.

I'm sorry, I must have missed the earlier post where you stated the 600 ohms balanced, not recommended with a tube preamp. So obviously you can only run SS preamps balanced. If you want a tube preamp you will need to run it unbalanced, obviously.

John

John,
Really sorry if I came across poorly. I certainly did not mean to come across negatively and truly appreciate and welcome your suggestions and feedback. This is my first time posting here because I am trying to learn ( at least a little... In all these years I have never owned a tube preamp, or a remote control :) on my systems so I am really venturing into new territory . My general principle has been simplicity of design (less parts, loops and interfaces) = less noise and better sound. I think the challenge for me is the number of quality components that are going to all balanced inputs and outputs with some making a concession to RCA outputs and inputs for convenience. ie in Stereophile measurements of the ARC reference 3 it was pretty obvious that measurements were better in balanced mode. I know measurements don't always tell the story but it's a start.
So thanks again for your feedback it really is greatly appreciated !

All my best,
Don

Hi Don,

No need for apologies, I'm just trying to figure out where you want to go here. It seems like you want a tube balanced preamp, am I wrong? Obviously your amp is a poor match for this, so you will need to either change amps, go balanced SS or single-ended if you want tubes.

FWIW, when you talk about simplicity of design, a single ended circuit is much simipler to implement than a balanced circuit, with approximately half the parts. So maybe it sounds like a single ended tube preamp is for you. There are many good single ended tube preamps out there, Shindo, Doshi, CAT, Joule, among many others. In fact, your choices amongst single ended tube preamps is far greater than your choices amongst fully balanced tube preamps.

If you wish you certainly could try a balanced tube preamp with your Threshold, nothing will blow up. The impedance matching is just to help the sound. With an impedance mismatch like you would be likely to have, would just make the sound rolled off at the frequency extremes.

IMHO you would be better served trying a nice single ended tube preamp with your amp.

Cheers,
John

BTW, I currently own a ARC Ref 3, great preamp. I can't say that I have compared the SE to the BAL though, as I've only run balanced. My amp has a 200K balanced input impedance though.