Pretty much you should take twice the dose you usually do with DXM HBr, but it will take twice as longer to kick in and last twice as longer.
So for example, if you usually trip on 500mg of DXM HBr, then do 1000mg of DXM Polistirex.
But then again, if you usually take 750mg of DXM HBr, then do beware taking 1500mg of DXM Polistirex, because this is a large dose and could possibly kill you.
Don't even use Delsym to trip though, it doesn't even work that good.
I wouldn't even attempt using Delsym to trip again, I've done it twice with 800mg Polistirex doses and barely anything happened. Stick with DXM only Robitussin (it can have guaifenesin just beware you may throw up) or find some DXM powder online, which is the best way to go.
However I do believe DXM Polistirex will bring 100x more euphoria than DXM HBr does, but that's the only real effect. For some reason the Polistirex version makes me VERY happy, but I have no idea why.