Why did you choose Input impedance of 1K Ohms for MC Low (60dB gain)? Recommended load impedance for most Low MC cartridges is 100 Ohms.
What is recommended varies widely. I have seen > 10 Ohm, > 20 Ohm all the way to very precise Resistance and Capacitance values.
The Zen Phono is designed originally as 99 USD entry level phono stage, which impedance based cartridge detection and automatic configuration of gain and load.
In other words a "phono stage for dummies".
The automatic configuration (with manual override if auto goes off wrong) was fully developed and tested, but deleted before release as "too advanced" for an entry level product, totally ignoring that the likely purchaser will be buying his first real turntable, cartridge and phono stage (after an all plastic bluetooth turntable) who has no clue how to set up a phono system.
Incidentally this is the "AI" that was somehow misapplied to the so called "elliptic filter" subsonic filter. That operates on the principle that the big subsonic noise is vertical from not completely flat (warped) records. Now for a number of reasons, vertical signals on the LP are in opposite polarity, to if you switch to mono the warped record related subsonic content disappears.
When cutting records, a so-called elliptical filter is used to blend low bass to mono. This is needed to allow the record to be cut. The "elliptical" comes from the oscilloscope picture of a stereo signal on X & Y. Mono shows a straight line, perfect channel separation and 100% pan shows a circle, which is not possible to cut at low frequencies. The "elliptical filter" keeps the oscilloscope picture "elliptical".
By selecting a blend frequency lower than the lowest setting of the "elliptical filter" for playback and blending ultra-low frequencies to Mono allows to preserve both the LF information cut into the record (in other words a warp/rumble filter that does not emasculates the bass response) AND the spatial information remaining after cutting the LP Masters.
Anyway, back to 1k loading at 60dB Gain.
The number of MC Pickups you might use with a 99 USD Phono Stage, even one that punches well above it's weight, is limited.
Basically the most likely MC's are Ortofon Quintet, Denon DL-103/103R and especially the Denon's; which in my view are among the absolutely best MC Pickup's ANY money can buy (if matched with the correct arm and installed correctly); work better with a 1k load than 100 Ohm.
While some advocate "no loading" and others advocate to impedance match the cartridge or even to use a virtual short circuit ("current mode"), I find modest loading is most likely to work universally.
Thor