In a desperate attempt to alleviate myself from audio torment, I started to play around with the iTunes equaliser settings. Turns out you can get reasonably acceptable sound from the built-in speakers. After much tuning, here are the settings I have set on iTunes.
Equaliser settings for the Dell S2715H monitor (using iTunes equaliser)
So if you do have this nice 27 inch full HD monitor and do not like the sound coming from the built-in speakers, perhaps you can try these equaliser settings. These should also work if you are on a Windows PC and using the same monitor.