Cooks Illustrated recipe too Salty
The first thing that caught my eye was the soy sauce. However, I think the real culprit here is the miso. 

From Wikipedia:


  Typically, miso is salty, but its flavor and aroma depend on various factors in the ingredients and fermentation process. Different varieties of miso have been described as salty, sweet, earthy, fruity, and savory. 


About red miso, from the same article:


  Akamiso (赤味噌) or red miso is aged, sometimes for more than one year. Therefore, due to the Maillard reaction, the color changes gradually from white to red or black, thus giving it the name red miso. Characteristics of the flavor are saltiness and some astringency with umami. It is often a much stronger-tasting miso. Factors in the depth of color are the formula of the soybeans and the quantity used. Generally, steamed soybeans are more deeply colored than boiled soybeans.


(Emphasis mine.)

The base ingredients for miso can vary widely. Also from the Wikipedia article:


  The ingredients used to produce miso may include any mix of soybeans, barley, rice, buckwheat, millet, rye, wheat, hemp seed, and cycad, among others. Lately, producers in other countries have also begun selling miso made from chickpeas, corn, azuki beans, amaranth, and quinoa. Fermentation time ranges from as little as five days to several years. The wide variety of Japanese miso is difficult to 
  classify, but is commonly done by grain type, color, taste, and background.
  
  
  mugi (麦): barley
  tsubu (粒): whole wheat/barley
  genmai (玄米): brown rice
  moromi (醪): chunky, healthy (kōji is unblended)
  nanban (南蛮): mixed with hot chili pepper for dipping sauce
  taima (大麻): hemp seed
  sobamugi (蕎麦): buckwheat
  hadakamugi (裸麦): Highland barley
  nari (蘇鉄): made from cycad pulp, Buddhist temple diet
  gokoku (五穀): "five-grain": soy, wheat, barley, proso millet, and foxtail millet
  


I would try a different variety or a mixture of more than one. An example from the Wikipedia article:


  Chougou (調合) or 'Awase' (合わせ) miso, or "mixed miso" comes in many types, because it is a mixture or compound of other varieties of miso. This may improve the weak points of each type of miso. For example, mame miso is very salty, but when combined with kome miso the finished product has a mild taste.


Do a little research and find one or more varieties of miso that suit your taste.