All, Thank you for the contributions to my question regarding by board layout (Thread:
Your help was very useful. I decided not to use any ground splits and used a standard 200 kHz step down switcher from linear, using the exact layout as in their eval board and sheilded inductors and LDOs to split the power. I did use LDOs at the output with ceramics, and that may or may not be causing issues (e.g. the bypass cap that linear says will reduce output noise causes the LDO to flatline- but is ok without it).
Also, I am yet to understand the workings of DACs. My ADI DAC (AD7302) running off +5VA has +3.3V digital lines coming into it and once supplies are powered up, the digital side goes up to 3.7V. ADI says it is a protection diode latching problem - however, I have used other DACs from ADI with similar topology with no issues. I moved the DAC to the +3.3V supply and things are fine. But what is its analog voltage output referenced to now? It does have an AGND and GND which are connected together close by.