You probably have windows that do not have Low E or argon, and trasmit
100% light. The real long term solution is modern glass. If you heat up
during the day you also radiate out heat at night. And with longer
nights in winter you have a net loss. I used to have a room like that
it went to 85, then froze at night. I replaced all glass and heating
bills and AC went down 17%.
Recording equipment produces heat, run you blower to distribute it.
Window film may help, but now it is free daytime heat. Shades or
curtains will help, but Cellular shades will add R 3.3, a great first
step to improving and upping efficiency of your house.