If you need the direct contribution of a Sun plus and hdr skydome, I also recommend you this workaround:
- Create an squared plane (9m x 9m) and apply an emitter material to it (1000000 Watts and 5777K color). You can apply a round mask to the whole material if you want to ensure its round shape.
- Put the emitter 1km away form the center of the scene. These proportions (9m side and 1km away produce the same sun aspect and size than the actual sun diameter at the actual distance).
- Parent the sun object to a null locator in the center of the scene just to be able to rotate the sun freely.
This way allows you to get the result you want (custom sun + hdr lighting), but the benefit is that you get it in the same render time (no need to launch a different render and then compose them).
In addition, you can enable MultiLight and thus have custom control over the hdr and sun intensities separately.
Even more: if you enabled Color MultiLight (take care of your Ram consumption), you could adjust the sun color as well.
And all of this in one render ; )
I hope this were helpful.