This is an opinion piece so no need to read and feel free rip me to shreds. There are people who diametrically oppose my view and I respect that position.
IMO, an amp/DAC is barely needed. It makes more sense to get a phone with decent sound. I've had phones that sounded plenty good enough for me with sufficient power for IEMs or HD 58X (IE: Blackberry Z10, Nexus 6s, couple of LG models...). Less equipment is better than more.
Even LDAC introduces loss, although only at bit rates beyond redbook audio. The point being, an external DAC/amp isn't purely an SQ gain.
There are two reasons I love the Q5K: mobility and PEQ
I've enjoyed a decent headphone experience while sitting in my office for years. The Q5K sounds about the same as my Topping stack (P50, D50s, A50s), however, being able to get up and walk to the kitchen for a drink or the bathroom for a whiz is a wonderful improvement. I don't understand why it's good to continue rocking out without interruption but it is. I can listen to an entire album, without interruption, while I am working, peeing, or fetching a snack. This is a perfect world.
I do worry that one day I will be listening on my wired stack and walk away without thinking about it, damaging a headphone cable. This hasn't happened yet, likely due to the fact that I haven't turned on the Topping stack in months.
To this end, the non-impressive plastic case of the Q5K must surely be a better bluetooth solution than the any of the beautifuly crafted and pleasure to handle metal cases of other high end portable DAC/amps.
I'm well aware audiophiles hate any form of equalization. That makes me a non-audiophile. I'm just a guy who enjoys good sound. When I equalize using the Oratory1990 curves, it's a big step up in sound quality on my HD 58X (and a tiny step up on my Sundara). If I was a purist, I would be listening on my living room 2 channel system from album and simply accept that I am a prisoner of my listening chair who can never accomplish anything in life. It wouldn't sound much better and where it does sound better, that is not due to PEQ degredation.
The Radsone ES-100 is an excellent device which served me well for years but it's GEQ isn't in the same useability league. The ES-100 is too fiddley for use with multiple headphones. Mine is permanently set for the HD 58X and it works very well for that. The way Qudelix integrated the Oratory1990 database (and others) as presets is brilliant. In a perfect world, they would also include house curves but they can easily be added manually using the custom saved settings.
I prefer the Q5K PEQ to AutoEQ on my desktop. I know they are essentially the same thing with the same result but the Q5K has it beautifully integrated.
Lastly, having more power than a phone can deliver is definitely a good thing. Most of the time, it's irrelevant but when I want to play a song loud there is a clear difference. I wouldn't listen to music while mowing the lawn using distorted sound from my phone but the Q5K can drive a pair of HD 58X as loud as I can handle so it doesn't have to work that hard to drown out the John Deere. The solid bass delivery of a powerful amplifier is a revelation.
I've read some comments the Q5K doesn't have sufficient power to drive Sundara properly. That may be true, and I don't specifically disagree, but it sounds great to me and it delivers all the bass and sound pressure I want. The Topping A50s has a lot more power but sounds about the same to my ears. Both can drive the Sundara harder than I would ever listen but I'm 56 and try to be gentle on my hearing.
IMO: Variance between DACs is miniscule to infinitesimal. Variance between amps is minor. Reducing impedance with a balanced cable and having the power to drive the reduced impedance is a significant improvement at high volume or heavy bass.
Back to the mobility point... I picked up a TP-Link AC1200 for long range bluetooth and now I can roam anywhere in the house glitch free, with local volume, and even local track change.
I'm loving this. Q5K is a slam dunk.
The two piece design doesn't seem robust and clear TPU both looks cheap and discolors quickly. As an alternative, I can heartily recommend the custom case I commissioned from @digitalazer
