Having waited for the Spectral phono long enough, and with no word yet or response to my voice mails from the factory, I will be evaluating the Sim Audio 810LP and the Pass XP-25 in the next couple of weeks, starting with the 810LP today. I have looked at those two extensively and they appear to be very well thought-out and designed units. The Pass appears to be purposely voiced a little forward in the presence region, with an intentional hump between 1kHz and 15kHz; the Sim appears to be designed to have no character. The Sim appears to be even quieter on paper and from reading the reviews.
There are a number of issues for me: with the Pass, the gain settings are too far apart; I need 60dB and they offer 53 and 66 (for balanced out); the loadings are also a bit far apart for the price range; I don't see them using those beautiful NAIS relays either, therefore I suspect the signal goes through the wires to the knobs and back - will find out soon; it also appears that you can't really place another component on top of or under the main unit (a problem I would have with the single-unit XP-15 as well). The Sim is very highly configurable, but the beefed-up power supply and isolation gel they use adds $5K over the 610LP, which appears to use the exact same circuit board. And for my XLR-to-XLR 'table to phono configuration, the Sim fits like a glove - the Pass, on the other hand, needs XLR-to-RCA converters that I am getting, but they might add noise. Considering that the Pass is also a fully balanced design, and having looked at the rear panel and circuit board, I think it is a mistake not to offer (and trivial to put in) additional XLR inputs, the way the Sim and my Ayre do.
I'll write up my thoughts as I go... Based on the phono card in the old Spectral DMC-20 I had, I have strong reasons to believe that, whenever their phono stage comes out, it will be superb. So any purchase now will probably be an interim solution... because of that, I can see me settling for the "lesser" and cheaper 610LP for now, which I may also evaluate if the 810LP lives up to expectation.