I would also agree with the JL subs, however, I would strongly recommend an electronics upgrade.
The Utopia BE will really benefit from the best in associated equipment they are very revealing. The Krell is a good integrated but in comparison to some of the even better integrated amps or separate components you can get so much more out of these speakers.
I would also say the same thing about the Benchmark great DAC for the price but there are so many even better sources.
So I would look at the system as a whole and make sure that adding a subwoofer will really get you all the way there.
The Utopia BE will really benefit from the best in associated equipment they are very revealing. The Krell is a good integrated but in comparison to some of the even better integrated amps or separate components you can get so much more out of these speakers.
I would also say the same thing about the Benchmark great DAC for the price but there are so many even better sources.
So I would look at the system as a whole and make sure that adding a subwoofer will really get you all the way there.