Sennheiser HD6xx + THX AAA 789 + ?

Audio noob here. Just picked up HD6xxx's and THX AAA 789 and the pair sounds fantastic but unless I max the gain knob they just simply don't get loud enough. I have a Sennheiser GSX 1000 gaming dac that I can output via 3.5 jack to rca or Scarlett 2i2 interface via balanced 1/4 to xlr to the 789 but don't have balanced cables for my HD6xxx. Debating on spending $70 on periapt cables for balanced output or $110 on a FiiO K3 amp to add to the equation but I don't know if it would diminish the quality running to the K3 to my 789 then to my headphones. Leaning towards the K3 though because I also have Audio-Technica ATH-AD700x's that I really like to use for some metal cause the drums sound so sick so I would benefit from the slight bass boost with the K3 as well. Thoughts? Would it be stupid to run from K3 to 789? Or is the balanced cable for the better headphones the better option? Appreciate it!!
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Nov 13, 2020
Just received a Periapt balanced cable for my HD6XX today. The 789's SE output was loud enough for me, but I spent a lot of time with the 798's pot around 12 o'clock. Running balanced brought the HD6XX up to a whole new level, not just for volume, but for sound quality as well. Everything is much more authoritative and dynamic. This is apparent even when I play music at lower volumes. In fact, I play most music below 11 o'clock on the lowest amplification setting now.
Jan 15, 2019
789 SE output is underpowered for HD 6XX. You need to change to balanced cable. Then you'll have no problems. Generally amplifying and amplified output is not your best bet. I'd look for an external DAC and balanced cable for HD 6XX.
Jan 15, 2019
Should have to turn up the volume/gain on the output of your motherboard. Go into the system device settings and make that change. It should help. I have the THX AAA 789 but am using an external dac. My 6xx have no problem outputting sound. My gain setting stays in the middle.
Jan 13, 2019
I am surprised that you aren't getting enough power from the single ended. Either I have really sensitive ears or your deaf (no offence). Because I got the HD 600 which is connected to my SMSL SU-8 DAC and I get enough power to drive them. I never turn them past 4 on the 2nd gain switch.
Jan 23, 2020
Same set up (SU-8 and THX 789) and I agree. No issues getting loud with the HD600 and it looks like they both have an impedance of 300 ohms. If I go to high gain anything past 10 o'clock it hurts.
Jan 13, 2019
  1. What's your source? Are you running it from a PC, phone, phono, etc?
  2. If you're not using the balanced out on the THX AAA 789 you're missing out on a lot. That amp's SE connection is just a** in comparison.
Aug 8, 2020
Yea your explanation went over my head. I’m still in noob status here. But what I meant by attenuation here was literally turning the windows slider down when the line out is plugged into an external amp. This would indicate an onboard motherboard dac. The reason I brought that example up specifically was to ask what the impact would be of the analog signal coming out of a dac/amp combo feeding an amp?
Aug 9, 2020
Apologies! I was quite tired when I wrote my original post. Basically, adjusting the Windows slider = digital attenuation. What you're doing is reducing the volume by effectively reducing the number of bits, thus lowering the total volume output in the end. So yes, the signal would be softer. However, this does mean as soon as you use any kind of digital attenuation, you've lost bit-perfect output period. In a very well-designed, well-implemented digital attenuator, the result might be audibly transparent, but bit-perfect it will not be. To make things more complicated, bit depth is only part of the equation. All digital attenuators use different math to reconstruct the signal between subsequent attenuations, and some (i.e. most) implementations are definitely audible, the Windows and Mac ones definitely included. What typically happens is that the music loses information; it sounds more "gray," uninvolving, and lacks details. It does not require anything close to a TOTL system to hear this; I heard this effect out of a Grace SDAC and a Schiit Magni 3 with an unmodded HD6XX. I wager this is audible even with off-the-shelf computer speakers (assuming of course that the speakers are active). So my advice is to avoid this if at all possible. But to answer your original question: yes, the signal coming out by lowering the slider will indeed be lower.