Imo protein is not the issue here. That conditioner is simply just too emollient for what you are trying to use it for. Quaternium-87 as the second ingredient?! No bueno. You are basically rinsing your hair with oils and other coating ingredients (the proteins are there to act in this capacity). This is the wrong kind of conditioner to co-wash with.
You need a cleansing conditioner that has actual cationic surfactants and emulsifiers in it that can clean the hair and won't build up, such as behentrimonium chloride, decyl glucoside, or cocoaminopropyl betaine. That conditioner has none (it looks like it would be very good at conditioning dry/damaged hair though just not cleansing it).
Have you considered using Curl Junkie Daily Fix, Devacurl No-poo or a product like that? Or even a VO5 or Suave conditioner?
4a/3c, fine strands, low porosity, medium density
Last relaxer: Jan 2010 - BC'd: 2/27/11