Thank you, that is helpful. I'm still not exactly sure how to actually implement that in 3dMEMA - would the code be something like this?
3dMEMA -prefix 2_by_2_example \
-set Condition_1_A \
Subj001 Subj001+tlrc'[A#0_Coef]' Subj001+tlrc'[A#0_Tstat]' \
Subj002 Subj002+tlrc'[A#0_Coef]' Subj002+tlrc'[A#0_Tstat]' \
-set Condition_1_B \
Subj001 Subj001+tlrc'[B#0_Coef]' Subj001+tlrc'[B#0_Tstat]' \
Subj002 Subj002+tlrc'[B#0_Coef]' Subj002+tlrc'[B#0_Tstat]' \
-set Condition_2_X \
Subj001 Subj001+tlrc'[X#0_Coef]' Subj001+tlrc'[X#0_Tstat]' \
Subj002 Subj002+tlrc'[X#0_Coef]' Subj002+tlrc'[X#0_Tstat]' \
-set Condition_2_Y \
Subj001 Subj001+tlrc'[Y#0_Coef]' Subj001+tlrc'[Y#0_Tstat]' \
Subj002 Subj002+tlrc'[Y#0_Coef]' Subj002+tlrc'[Y#0_Tstat]' \
I know this must be missing something, because there is no way to tell that 1A and 1B are levels of the same condition (same for 2X and 2Y)
P.S. - I believe the page you linked me to might be the one that is supposed to be linked in the output of 3dMEMA -help, but that link is currently broken (https://afni.nimh.nih.gov/sscc/gangc/MEMA.html).