Actually, as I said, you can get a new Softone 4 for $425 US plus the cost of shipping and currency conversion.
Simply go to the Softone website and choose to pay in Japanese yen, rather than US dollars. The price is 68,000 JPY, which converts to $425 USD. Softone can send you the invoice in JPY and pay with PayPal, or bank transfer in JPY. Both your bank, or PayPal, will automatically charge you for currency conversion, currently on the order of an additional 4%. Surface shipping is 6,100 JPY, or $38 so that will cost a total of $463 and add in the 4% for currency conversion and you are all in for $482, inclusive of shipping, no need to pay $800. Or roll the dice buying used.
On the other hand, I think that the 834 is the better choice for you, as the Softone is not particularly tubey and doesn’t soften the sound as much as the 834.
When I do the math out long, I get a SUT gain of 24db in low and 27db in high, corresponding to impedances of 183 and 94 ohms, irrespective of transformer losses, or resistive loading of primary, or secondary.
https://softone.a.la9.jp/english/Model4/M4-2.htm
Using the formula of preamp load impedance divided by turns ratio.

