It more has to do with the style of production. Synthesizers were in large use throughout the 70s and 80s. The HD540 have no problem reproducing synthetic sounds. Inherently, acoustic sounds and timbres are much more complex. The accuracy of the HD540 can present an uncoloured (in other words 'not smoothed') version of synthesized sound, which for some recordings, may sound harsh. Not the headphones fault, it more has to do with engineering and mastering. Enter the 90s later electronic era, and there are many recordings that aren't up to par. At the same time there are many excellent electronic recordings. For instance, take any Trentmoller album and the HD540 will sound superb, though perhaps lacking bass for some tastes. Still, I get why you may want something a bit smoother up top, and the HD650 certainly fits the bill. I haven't heard, but you may want to check out the HD545, HD565 design. It is from the era. Here you can compare HD560 with HD565 https://www.innerfidelity.com/images/SennheiserHD560OvationII.pdf https://www.innerfidelity.com/images/SennheiserHD565Ovation.pdf You can see how the 565 slightly warms up the top end. Whereas the 540 and 560 were designed for true to life reference, the 565 were more forgiving. Later on Sennheiser sound would incorporate a bit of both. If you aren't adverse to the fit of the HD650, the Massdrop HD58X is going for a good price at the moment.