After writing about how niacinamide helps reduce the "jitters" of caffeine, especially in high doses, I did some research on theanine and in the process I found quite a few studies claiming synergism between the two and that theanine also helps restrain the nervousness that caffeine may cause in higher doses. So, maybe not a bad addition to the niacinamide/aspirin/caffeine combo, especially given theanine's anti-serotonergic effects and caffeine's dopaminergic ones.
http://www.ncbi.nlm.nih.gov/pubmed/10737183
"...Next, the stimulatory effects of caffeine were inhibited by an i.v. administration of theanine at a level higher than 5 micromol/kg (0.781 mg/kg) b.w., and the results suggested that theanine has an antagonistic effect on caffeine's stimulatory action at an almost equivalent molar concentration."
http://www.ncbi.nlm.nih.gov/pubmed/10737183
"...Next, the stimulatory effects of caffeine were inhibited by an i.v. administration of theanine at a level higher than 5 micromol/kg (0.781 mg/kg) b.w., and the results suggested that theanine has an antagonistic effect on caffeine's stimulatory action at an almost equivalent molar concentration."