I am not sure about when your brain switches over.
I was lucky, i learned English as a small toddler so I never translated in my head. When I learned French, it was natural to think in French. I have met people that after 30 years speaking English in Australia, still translate from their original native non-English lanaguage...
Maybe it's a thing you do consciously and jump into the void and hope and after a while it becomes second nature.
As to my Italian... I never studied it properly so my grammar is woeful. Accent and vocabulary is not so much a problem as I have two other romance languages, Spanish and French, and I even studied Latin at high school.
But I picked up Italian here and there and have never spent any time seriously trying to get it right ( a low priority as I mostly use it in Italian restaurants!). If I did it, would improve heaps in no time. I got the hand mpovements down pat! 
As to the brain channels...
I am not sure. When I speak in English i often get words in Spoanish or French come to mind while I am still thinking in English. So if it is a channel the signals get confused at times.
What I have noticed is that if I use Spanish words while I am speaking English I will pronounce them with an English accent.
Then again I always count in Spanish, as my wife once told me, without being aware of it. I can easily count or do maths in English but I must make a conscious effort to do it. If I don't think about it I will naturally revert to Spanish.
Be aware that I not only learned Engl;ish before I went to school but I also followed a bilingual education. I went to English school in the morning and Spanish school in the afternoon studying often the same subjects in both languages. My parents spoke both languages and often spoke to me in either of them. So I don't know why the counting in Spanish is so strong.
As to your problem, I would suggest you take a plunge and try and think in Spanish. Do it consciuously at first and see if it becomes unconscious with time. don't worry about getting it right all the time. Just speak it. Remember that the four stages of learning are:
1. Unconscious ingnorance (you don't know what you don't know.)
2.Conscious ignorance (you know you don't know)
3. Conscious knowing (it takes an effort to use the skill)
4. Unconscious knowing (you use your skill and you are not aware of it.)
think of learning to ride a bicycle or driving a car for the four stages to become clear.
Hope this helps.
R