@Wong *******
I have seen people who left the country on an un-canceled ED extension, who got a NOn-B visa, who came back to thailand and then 2 months later when they went to extend their Non-B the immigration officer noticed they'd never canceled their ed extension and they were fined the 20K baht maximum overstay fine (even though they'd left the country BEFORE their old extension expired, gotten a new visa and came into the country on it).
Go cancel the ED extension as soon as you get back on your new visa.