While many early compact discs suffered from a shrill, brittle sound, this turned out to be because many albums were originally mastering with a high-end emphasis, typically called an RIAA curve, which was required when transferring to vinyl. Once engineers went back to the original recordings, that issue was largely resolved. But for many, this was enough for them to write off CDs as harsh and cold.
For the most part, today’s digital recordings sound pretty darn good, but there’s often an issue with the high end. In many cases this can be traced to relying overly much on boosting the high-frequency controls to add presence and make individual instruments “pop” more.
Rather than cranking the highs to bring out a track, look for ways to provide each track with its own pan position and frequency range. Try to sculpt the tracks so that they layer nicely on one another, rather than fighting for the same frequency space.
In fact, with the best mixes, if you solo individual tracks, you’ll be surprised how odd (or even BAD) the tracks sound. This is because the mix engineer has worked to make the tracks sound good in context with all the other sounds, rather than working on them focusing on making them sound good on their own.