Promix is top quality. I have ever grown in TLO, or supersoil, as some like to refer to it by. I have grown in hydro and hempy style. Promix is by far the easiest to use with the best results for a beginner. Even for advanced users, it is hard to beat for returns on the least amount of work which is why I use it a lot. It is a very forgiving medium with very little hassle. Out of the bag, it is going to be around 6.6 and you will want to water it with 5.3 the first couple of times, after that you can generally set it at 5.8 and run with it.
I will be completely honest, I have never used AN for personal reasons. I think they are an overpriced scam that preys on newcomers to the craft. There are a lot of nutrients out there that are much more cost effective. Regardless of opinion, yes, I can guarantee you are going to have to ph your solution. If you use rainwater, RO or distilled it won't be as bad but if you use tap water there is no way around it. Tap water has too many buffers in it and will raise your ph no matter what nutrients you use.
Hope that helps bro and best of luck with the grow. With you researching ahead of time I am sure you will do great.