It’s a neutral reference headphone, an open back headphone that’s meant to play the audio with very little change to the sound as it was recorded. This is the trend of open back headphones and what makes up the majority of “audiophile” style headphones these days, they’re primarily judged on their neutral listening chops, how adherent to the Harman curve they are or can be, tuning and technicals. Rather than accentuated bass and highs like a V-shape or a Harman-tuned pair, it aims to represent bass, mids and highs accurately with their intended prevalence. For the purposes of a neutral listening reference audiophile headphone, the HD600 is among if not the best in the world.

The Porta Pros are a warm bass-rolled open supra-aural headphone. They’re doing two very different designs meant to do very different things. They are not known for being neutral and instead have a throwback sound you’re unlikely to find duplicated elsewhere as supra-aurals are few and far between. If you’re looking for something with less highs and more bass, you could look at headphones with a V or U shaped signature, or something balanced that isn’t as dedicated to neutrality.

You can try using EQ to adjust the 600 to taste but it will never have a bassy sound nor will it shy away from the sort of sterile and clinical reference vibe unless you really lean into changing it up and at that point, you’re better off getting a different pair of headphones. The 600 costs what it costs and has its reputation based on what you’re hearing, its ability to do that type of sound. You could likely sell or return them, research headphones that may have a signature and style more to your liking - AKA not an open back neutral listening headphone or a blind buy based on generalized reputation but from its measurements compared against your preferences - And get better results than trying to change the 600 beyond what some reasonable amounts of EQ can do for them.