Hi Jon47,
I haven't heard either the 610 or 810. Usually when Simaudio has products say like the P-7 pre and P-8, you almost get all the performance of the highest model at a significant price reduction.
I almost at the time of buying the Zesto, had the E03 on the short list also. The reason I didn't buy it was for the same reason you have stated.
I will be burning in the 610 for 2 weeks. The Simaudio equipment has a very long break in time I have experienced first hand many times.
The dealer is checking today to see if they have a 610 in stock since they are so new. So, it may be a while before I report back especially with the break in time.
The Zesto sounded good, although the SS 610lp will be more my cup of tea. There is an 810 on ebay for $5K, although it didn't look well cared for.