I think that circuit cropped up in another thread a few weeks ago. It has so many weaknesses I can only assume it was designed by someone who was new to valves.
Two things I noticed so far without doing anything to the internals. When using a SUT, sound changes drastically. Transformation was from OK to really nice. I think this constitutes to the fact that the input of this phono is not properly loaded for MC cartridges. I am using a DL103 so 100 ohms resistor in the input would change the sound I believe.
Replacing 12AU7 to 12AT7 changes the sound positively. Assume it is because of the difference in gain of two tubes.
It won't have enough gain without the SUT using a LOMC like a DL-103, so just leave the loading at 47k.
There are a lot of lousy sounding 12AU7's out there. 12BH7 would be a better tube, but draws double (IIRC) the heater current, which could be an issue for the PS trans.
You might find the link below to be of interest, it describes a conversion of the phono stage
(if I understand correctly) of your amp.
http://homepage.ntlworld.com/lez/Yaqin MS-22B/Putting 'Life' into the Yaqin MS-22B.pdf