My so called "audiophile" Senn HD6xx/650 cans are far from it...There is no depth. (Mids and highs are nice).
Apart from classical music with very large orchestras, audiophiles are more likely to listen to music that doesn't have a lot of low frequencies apart from enough of a hard hit from the bass drum on some jazz tracks, and obviously if they're listening to vocal tracks, well, having clear and sweet midrange and non-fatiguing highs are what they'd be looking for.
That said, I EQ my HD600 to follow the HD650 curve above 1000hz. I don't boost the 40hz to 120hz region to match the HD650 though, just a boost to everything below 50hz because that's where it trails off.
My so called "audiophile" Senn HD6xx/650 cans are far from it. They require some EQ to add just enough bass to appropriate level. I like articulate, musical, just enough bass, not overwhelming amounts or anything like that, but the HD650 has no bass extension and is somewhat lacking of the appropriate amount of lows. There is no depth. (Mids and highs are nice).
If you have Neutron Music Player:
Band 1
Center Freq: 35hz
EQ type: Low Shelf
Q Factor: 1.0
Gain: 3dB
On any other EQ: Just boost anywhere well below 50hz. If you boost at 50hz you'd be boosting where the response is still strong and you get even more auditory masking even if the Q-factor is relatively wide.
My Status Audio CB1s at a fraction of the price blow the Senn HD6xx away.
It's actually difficult to design a driver that has a very wide yet very smooth response curve that also needs to be easier to drive, requiring no amp or at least not a monster of an amp, while staying relatively affordable as to be profitable. Which is why Sennheiser can do better on the rest of the range but can't make sure that the response doesn't trail off below 50hz.
If you want something that really reaches deep into the bass and has a flat curve from 10hz to 1000hz, there's the HE400i. Just note that, like what I noted above, the trade off with that is comparatively jagged response above 1000hz and markedly lower sensitivity.
On top of all that, your CB1 are closed back, and if it also has waaaaaay bosted bass to compensate for how headphones need overboosted bass to some people because even if they measure similarly to a speaker will always feel like they have less bass since the bass isn't radiating all over a room. Perception therefore is that it's weaker because you don't feel the bass bouncing off the walls (ie it won't sound deeper), kicking you in the chest, crawling through your skin, etc.
Basically you're dealing with the main problem of it being a headphone and then the open back allows for ambient noise to get in the way even more. Even a spposedly "quiet" room can still have a total noise floor of around 40dB, you just don't have any distinct sound source that sticks out.
So far I have plugged them into a JDS O2, Schiit Magni and direct to a Marantz CD5004 and just can't get the low end to kick in. I'm thinking these cans may require EQ.
I don't listen to my computer, so software EQ is out.
I would like to find an amp with some EQ built in (that is not the Bravo thing). If that type of thing is not available, perhaps you can tell me how I can add a separate EQ unit to one of the amps I listed or the CD player at least.
What are your recommendations please.
Use a computer or smartphone and run software EQ because hardware EQ might not have the right settings. You can end up boosting the frequencies that are already loud, which means you'll either not get past auditory masking or get wobbly bass.
If you don't want to change the source you might be better off using a different headphone. if you want to maintain the midrange of the HD650 but get deeper lows, there's the LCD-2C.