I have this harp and I do like the sustain very much, but it’s definitely not always desirable. I am working on a number of Christmas pieces for church this year and know just what you mean about the sound running together.
A lot of times I have to stop strings going in using my knuckle or fingertip before playing the next note. It works as long as I use a firm, frank touch – if you’re hesitant, those bass strings will keep ringing, buzz or sound a harmonic if you’re in the right spot.. Yes, you can play more softly sometimes, but it’s better to have the control of learning a few ways to silence your strings individually. I suggest you ask your teacher – or a guitarist friend – to show you some muffling tricks if you like the harp in every other way.