I am usually pretty uneasy leaving the volume to the max because I am always afraid of the DAC clipping at that level however I have tried it multiple times and it does not seem to be the case besides Wolfson would be warning the implementers about running it at that level.
Having said that, I usually leave it at 235 and let the amp take volume control.
If the amp has a decent output, the level you leave the dap at does not seem to make any differences on SQ but the amp seems to have a sweet spot so use the amp in combo with your dap and leave it to your ears to appreciate it and find your own sweet spot.
Thanks for the input from both of you. I decided to give the O2 from JDS labs a second look. This time I made an arrangement with the local audio shop. I want to give this amp a thorough test drive with DX50 and she agreed to me taking the home and return it in 3 days before I buy it.