It seems that most caudates are adaptable to a wide range of pH conditions. I don't speak as an expert on this, but I would imagine Cynops ensicauda would do fine at any reasonable pH (6-8 or so) as long as it was properly acclimated to it.
pH can be difficult to change. Many products sold at pet stores are strong bases or acids that can greatly shift the pH, which can be quite stressful to the animals. I wouldn't recommend these. Also if you have a high kH, it's natural buffering capacity would keep the acid from having much of an effect.
Other methods of lowering pH include adding peat moss to the filter or placing pieces of driftwood in the tank. Both of these add organic acids to the water and lower the pH slowly. If you have high kH water as noted above, diluting your tap water in reverse osmosis or distilled water can lower the kH and often the pH. If the pH doesn't change it is now more readily changed by weak acids.
Honestly, I don't think you need to worry too much about pH, the newts should be able to adapt. Someone else may be able to tell you more.