SQ lacking

I have a pair of Sennheiser HD600s. I recall finding them muffled sounding and lacking high end extension when new. Dozens and dozens of hours later and a cable upgrade (to Senn 700 or 800 cable?) they sound much better. Have to say though, they don’t have the sparkle of the AKG550s but then the AKGs are light on bass compared to the Senns. After time for break in, consider a Schiit Loki for equalization if things don’t improve to your total satisfaction.

Sennheiser 600s definitely sound clearer and better all around if you remove the grills and foam. It’s the only way to fly. 

Something is wrong. You should be enjoying crisp clear sound.

You might want to further describe your system (cd transport - dac - preamp - headphone amp). You say you have a dac/headphone amp. You should be able to connect your cd transport to the digital in on your dac/headphone amp and plug your headphones in and be good to go. You don’t need to take the analog out and run it through a preamp.

If you’re not having some kind of connection problem, get back to whoever you bought your gear from and seek advice on your system and try to isolate which item isn’t working properly. If you can’t find the problem, return the gear.

Thank you everybody. I will outline my system:

1) Wells innamorata power amp
2) Jolida Fusion Preamp
3) PSB Imagine T3 speakers
4) Simaudio 380D DAC
5) PS Audio Perfectwave CD transport
6) Questyle CMA 600i headphone amp/dac
7) Musical surroundings nova phonomena phono preamp
8) Lumin D1 streamer
9) Melco N1A network digital library
10) Project Xtension 10 turntable
11) JT Dynamic Power 4 rail power supply
12) Dspeaker antimode 2.0 dual core room correction
13) Sonos connect ZP90 streamer
14) Shunyata MPC-12C power conditioner
15) Focal elear, final audio design sonorous VI, Sennheiser hd6xx, hifiman he4xx, Beyerdynamic dt880 headphones
16) Virtue audio interconnects, JT Dynamic Power power cords

That is everything that is pertinent. I just started listening, and just the cd transport with just my speakers and my Sennheiser headphones. Looking forward to streamer and turntable, as well as other headphones, but I was rather surprised at the lack of any wow factor when I put on these headphones. Tomcy6....so, my current chain is cd transport-dac-preamp-headphone amp/dac. You think that could be it? So do away with the dac and preamp and it could make a big difference? I am a truck driver and currently out on road...but can put this to the test this weekend

Oh, I think maybe cd transport-dac-preamp because if I go directly from cd transport to headphone amp then I can't listen to speakers without having to disconnect interconnects all the time?