I just got another A30Pro/D30Pro stack in today (had them individually but not together). With optical they sound great, and I have two heavy hitter headphones to see what limits it has when equalizing and doing a preamp reduction. The A30Pro temps measured in the center at 107f and 105f everywhere else. If you hold your hand 2 inches over it you don't feel any warmth, and the DAC doesn't get warm, so I put the amp on top to let the vent holes do their job.
It got the Hifiman HE6se plenty loud in medium gain, but you need high gain at -4db and at -6db you'll be out of gas for pre-volume war recordings if you equalize them. -4db seems to be the practical limit for this combo and fun volume levels for a favorite song every once in a while to stab the volume wheel. The Beyerdynamic DT880 600 ohm fared better, but for older songs with more than -4 it'll be loud, just not extremely loud. To be fair, the A90 I have here isn't without limits on the HE6SE either. I see why people use speaker amps with banana clips for it, but I'm not that much of a risk taker.
I'm keeping this stack as a daily driver as I'm tired of buying balanced cables for other amps to get full power. Also an amp shouldn't determine what headphones you buy, or have to send your beyerdynamics out to an Etsy vendor at $125 a pop with shipping charges. I have the stack with the review recommended filter 6 and using the optical and the noise floor is spooky quiet... Best part of this combo is what it doesn't have. No MQA or Bluetooth antenna, which I would never use anyway. I also like the power cord on these, the same ones you use for a computer, so it's easy to replace with a longer one if needed.