For Blaziken GX's "Blaze Out GX" attack, can I choose to discard two DCE's if I want?
Yes, you can choose to discard one energy from each of the two DCE's, resulting in both cards being discarded.
Source: Celestial Storm FAQ (2018-07-20), TPCi Rules Team (2018-08-02)

Relevant cards

Note: All applicable cards may not be listed below.
SM7_153
SM7_170
SM7_28