Looking for upgrades (6XX & o2 ODAC)

I currently have a Mayflower o2 ODAC and a Sennheiser HD 6XX. I’m currently looking to upgrade my headset and maybe my DAC/AMP in the future this year.

Use Case: I presently use my headphones for general audio listening, gaming (FFXIV, assorted gaming from retro emulators, Halo MCC, yakuza games, Resident Evil, etc) (Mostly single player games.)

Preferred Music: I listen to mostly rock and metal (CCR, Beatles, Slayer, Slipknot, etc) and rap (late 80s to early 2000s stuff). (Run DMC, Eminem, Geto Boys)

Source: I use an USB cable as the source for the o2 ODAC and would like to keep using USB as my source.

Budget: 100 to 200 for a new DAC/AMP and 150 to 200 for a new headset

What I’d like to improve: I like my HD 6XX but I’d like to get something that offers a bit more bass and punch. While I know Sennheiser is known for its neutral tone I’d want a headset that makes playing older games or JRPG music pop more and is just overall a more fun headset but still has a good balance. I currently have my eye on a beyerdynamic DT 770 PRO 250 at 170 on amazon. I’m down for suggestions for what’s a good headset for Single Player gaming and music listening.

As for my amp I’m curious if there are any Amp/DAC combos for under 200 that’ll be a huge improvement over my current o2 ODAC that work with USB input.

Most closed-back headphones in the same price range should give you more bass. DT-770 has pronounced bass and treble, which may make cymbals feel sharp coming from the Sennheiser pair. Audiotechnica ATH-A990Z may be worth considering too.

For the odac, does that have a line-out that could be connected to an external headphone-amplifier?

The ODAC is an amp / dac combo