Elise,
The clock - either the G0s or the G0rb will make a nice improvement - it adds a level of refinement to the sound but it is more on the subtle side. I think your plan to initially get the P03/D03 and use the clock in the D03 to clock the P03 transport is the correct approach. Then demo the external clock at a later time. When you do demo it, I'd recommend leaving the clock in for about a week and listen. Then remove it - you should hear the difference and then you can decide if the improvement you hear is worth the additional expense.
As for how the P03 D03 compares to the one box Esoteric players - I did own the X01 and then the X01 Limited models. The P03 D03 is a significant step up - it has a more organic and liquid sound, is more refined, has better resolution, has a wider and deeper soundstage, etc. I have not heard the X01 D2, but I would bet that the X01 D2, while better than the X01 limited, is closer in sound to the X01 limited than it is to the P03 D03.
The clock - either the G0s or the G0rb will make a nice improvement - it adds a level of refinement to the sound but it is more on the subtle side. I think your plan to initially get the P03/D03 and use the clock in the D03 to clock the P03 transport is the correct approach. Then demo the external clock at a later time. When you do demo it, I'd recommend leaving the clock in for about a week and listen. Then remove it - you should hear the difference and then you can decide if the improvement you hear is worth the additional expense.
As for how the P03 D03 compares to the one box Esoteric players - I did own the X01 and then the X01 Limited models. The P03 D03 is a significant step up - it has a more organic and liquid sound, is more refined, has better resolution, has a wider and deeper soundstage, etc. I have not heard the X01 D2, but I would bet that the X01 D2, while better than the X01 limited, is closer in sound to the X01 limited than it is to the P03 D03.