Although there are many possibilities, the Monster digital could be the culprit. What is the rest of your system comprised of? Also any recommendations that we could offer would depend on the degree of brightness you want to alleviate.
A reasonably priced digital IC I feel is smooth, open and throws a massive soundstage is the Acoustic Zen MC2. An overall excellent cable. Also, the analog IC from your DAC could be a factor, and for that I would recommend looking into Cardas Golden Cross. A very warm and full bodied cable with decent imaging and detail.
Is the DAC1 you're referring to the Bel Canto DAC1? If so, it's hard for me to imagine that unit being the cause of the brightness as that model had a reputation for being quite smooth.
A reasonably priced digital IC I feel is smooth, open and throws a massive soundstage is the Acoustic Zen MC2. An overall excellent cable. Also, the analog IC from your DAC could be a factor, and for that I would recommend looking into Cardas Golden Cross. A very warm and full bodied cable with decent imaging and detail.
Is the DAC1 you're referring to the Bel Canto DAC1? If so, it's hard for me to imagine that unit being the cause of the brightness as that model had a reputation for being quite smooth.