Can the MV88 be used to record soft sounds?
It all depends on how soft. The MV88 was designed primarily to record loud sounds, like a rock concert, or medium sounds, such as conversation.
As the sounds gets softer and/or the MV88 is placed farther away from the sound source, at some point the self-noise (hiss level) of the MV88 might become noticeable or objectionable. With the MV88 set for maximum gain, the self-noise level is around 25 dB SPL-A. This is similar to a Shure "live sound" microphone like the Beta 98A.
The MV88 does not have an exceptionally low noise floor like a Shure KSM44A (4 dB SPL-A), however the KSM44A is nearly seven times the price. If the requirement is to record very soft bird sounds in a forest, or the barely audible whispers of wind in the trees, the MV88 may not be appropriate.