Taz777, could you plug your headphones directly in the DX3 Pro, without headphones amp, and test it like that?
Because the headphones amp of the DX3 Pro is said to be very good!
I tried this today and listened to a few songs from Tidal HiFi. The DX3 Pro was put into headphones mode with volume set at -38dB (<-- very important to set the volume low to start with BEFORE plugging in your headphones!). I used my AKG N40 IEMs with a fairly decent MMCX cable.
I played three HiFi tracks from Tidal, and one Masters track.
Initial impressions are that it sounds pretty good! There is a good amount of bass. Treble is slightly subdued, but that may be the IEMs. Layering is a not as much as I'm used to. Increasing the volume to -30dB makes the music quite loud, but also adds a little more dynamics to the sound. Vocals are just ever so slightly 'cloudy'. There's a pronounced mid-bass underlying every track that can sound good or bad depending on the song.
It's a very comfortable sound to listen to. I have a much higher resolution dedicated headphones system so I'm comparing against that, so some of the criticism may be a little unfair.
All in all, for what you get for the money, the DX3 Pro's headphone output is pretty good. It doesn't quite grab me or amaze me, but is pleasant. I could listen for hours so it's not tiring. The overall signature is 'rounded'. It could do with a little more dynamic range.
I don't think anyone would be disappointed with the sound quality from the headphone jack of the DX3 Pro given just how much capability is packed into the little unit at such a great price.
I'm happy to try one or two other headphones if you want me to as they may match the DX3 Pro better than the AKG N40s.