IV is the last stop, end of the road. There is no potentiation beyond IVing it. Be very wary of trying this unless your willing to risk a lot of your near future to binging on it. Its incredibly compulsive and addictive. That being said, its pretty damn fun if you enjoy MDPV. Be careful.
I wouldn't take very many other substances with MDPV. Its pretty strong and pretty hectic and things could get out of control fast. If anything, maybe opiates, GBL, *LOW* dose benzos, or light drinking.
Adding more stimulation to MDPV should be undesirable.