Manley Chinook with (very) low output MC ZYX?

yep, that is correct. not in signal path but are DC servos for FETs.

lowers the noise floor a ton. The other thing you can do is change out all the loading resistors on the back panel to Vishay VSRS.  just like focusing the looking glass much better imaging, quieter backgrounds and micro dynamics much better.
I would attach some photos but can't do it with Agon forums.

I agree that Vishay nude resistors (I don't know about "VSRS";  I do know about nude TX2575, which can be ordered on-line) will be superior to the stock phono load resistors in the Manley phono stages.  The TX2575 are superior to just about any resistor ever.  However, on the subject of the op amps, was there ever an audible "noise floor" to begin with?  I find the Steelhead to be intrinsically very quiet even at full volume.  Further, in most cases where there is an op amp used as servo, the device is bypassed by a capacitor or two, just for that reason to render the op amp inaudible.  When or if the op amp is intrusive, one cure is to increase the value of the bypass capacitor(s).  But I don't hear it, assuming the Steelhead, like the Chinook apparently, uses op amps as servo.  Finally, the Steelhead is so full of parts that I am loathe to get in there with my soldering iron, except to change the phono load resistors, and in my case to change the output stage, since that part of the circuit is quite accessible.  A lot can be achieved with a little effort on the output stages.

This is the manufacturer of Vishay resistors:
Texas Components on ebay, i bought from them many times