Sertraline/Fluoxetine vs DXM for MPA tolerance reduction?

[SquidInSunglasses]

I recently acquired some DXM after reading the speed tolerance reduction thread ( http://www.bluelight.org/vb/threads/97021-Speed-Meth-tolerance-prevention-reduction-long ) that stated DXM is effective in reducing the formation of tolerance due to amphetamines. However, the drug combos FAQ on here, the TripSit combo guide and the DXM bottle reccomend not combining DXM and SSRIs due to risks of serotonin syndrome. On the other hand, the user in the thread linked above and the workers at the pharmacy seem to think that it is not risky to combine the two. So my question is, first is DXM likely to work in reducing the formation of tolerance to MPA, and second for low doses of SSRIs (50 mg of sertraline, about to taper and start 20 mg of fluoxetine) how much risk of an adverse reaction is there for a low dose (roughly the medically reccomended 20 mg per the advice in the thread linked above) for me?