@mrbungle and
@Veri - I received my DX7 Pro + A90 bundle yesterday, a day earlier than expected. I've spent the last day testing and becoming familiar with both devices. In my case I'm glad I opted to add the A90. While the DX7 Pro does a decent job on its own, I found it underwhelming for my SDR modded HD800 with Dekoni earpads. The HPA in the DX7 is more than ample for my Fiio FH7 and Shure SE846 IEMs, as well as my Hifiman HE560.
The HD800 itself is known to be a finicky can to pair with. The A90 handles it superbly, using Audirvana on my MacBook Pro with the Sonimus Soneq equalizer plugin. I don't need a full equalizer as I've never been bothered by the 6KHz peak that the HD800 has. I may still look at some op-amp rolling for the DX7, but for now I'm happy with the A90 for the HD800.
I had an 'ooops' moment when I couldn't get it to pair with any Bluetooth sources. Turns out I 'forgot' to install the Bluetooth antenna - it fell out of the box during unpacking, hit the floor and from there my cats made sure it was pushed far under the bed. Out of sight, out of mind. During troubleshooting I realized the antenna was missing so I went back to check the packaging and eventually found it under my bed.
Otherwise, my only other minor concern is that the DX7 Pro doesn't like my normal USB hub that's connected to the MacBook Pro. I actually have two hubs - a uGreen USB3 hub with integrated 1Gbps NIC that's velcro'ed to the MBP and connected all the time for the NIC. I then have a no-name brand USB3 hub connected that has worked well in the past with other USB DACs, but not the DX7. If I connect the DX7 directly to the MBP or to the uGreen hub, it works fine.
I'll want to keep on the lookout for a replacement hub that works as direct connecting or using the uGreen hub is a little kludgy when I'm using the MBP on my lap. Any recommended hubs from anyone? I know direct connection is preferred, but it's just a little inconvenient when using a laptop.