I have a McIntosh D100 which is the same as the D150 except the dsd capability and it doesn’t certainly suffer from weak bass and overly emphasized treble as you describe on the contrary the bass is tight and powerful ,the treble is natural and smooth. Before blaming the DACs you tried maybe you have problem with your sources,cables or amplification which cause the weak bass and bad treble.
Another point, the Harbeth in general are great speakers but tend to smooth gentle bass (which is very good IMO) and if you are looking for rubost/aggressive bass you will not
get it from your speakers and also the Harbeth’s are very revealing speakers (this is a good sign how good they are )so are not forgiving to poor recordings . It doesn’t matter which DAC you buy rubost bass and forgiving to poor recordings just not going to happen.
Another point, the Harbeth in general are great speakers but tend to smooth gentle bass (which is very good IMO) and if you are looking for rubost/aggressive bass you will not
get it from your speakers and also the Harbeth’s are very revealing speakers (this is a good sign how good they are )so are not forgiving to poor recordings . It doesn’t matter which DAC you buy rubost bass and forgiving to poor recordings just not going to happen.