Hang on a second, the technical ability of the Sundara far exceeds the DT-770.
And the 1770s sound the same as the 770 - the price increase is in the quality of materials.
The 6XX has great mid performance and is a sound microscope, but yes, no sub bass (or extension in the highs really - or soundstage width).
The Sundara out of the box is very bass light, but as mentioned by @lrjshabaz, they respond well to EQ and do everything better (except those weirdly good mids from the 600 series) than both cans.
Instead, consider the Fidelio X2HR. Far more musical than the 770s, more engaging (though less technically accurate) than the 6XX and can do bass even though it’s open.
If you can afford it however, go onto Ebay and look for a used Fostex x Massdrop TH-X00 or TR-X00. I have the Purplehearts edition which is extreme V so probably not recommended for most, but the other two are less extreme, the Mahogany seems to be the middle ground choice.
They have a resolution increase over the entry level (basically in my experience anything below £400 - funnily enough, except the Sundaras which are stupidly good resolvers for the price) and actually play the lower region of the frequency response with authority (which of course, whilst well extended, the Sundaras do not).
They’re not mid forward however, and really benefit from a pad upgrade (Dekoni Hybrid Elites are my favourite) for comfort - well…to stop sweat and to keep it from moving on your head, sound is the same.
I had the same rattle with the 770s, tried to replace the driver myself, but ended up piercing the bloody thing with the screwdriver when I was trying to release it from its housing
So yeah, give it to a pro and the turn around is usually quick. Sometimes you don’t even need a driver change, you just need to remove the hair that’s stuck in it.
So to recap:
- I’d recommend trying the Fidelio X2HRs before going up the food chain.
- If you get the Sundaras, prepare to EQ if you want to get some sub bass out of it - but yes, it’s a seriously good headphone for the price, even if you get a bad one, just reach out to Hifiman, their support is usually excellent.
- You probably want to skip the Beyers if your primary objective is listening to music, unless you get the 1990s and aren’t afraid of a treble peak. For gaming and movies, they’re still my brand of choice though except for the Heddphone and the higher end Audezes (actually even the Mobius is impressive in this field).
- You should be able to get the 770s repaired without too much issue.