First off ANY steroid suppresses natural testosterone production, period. Some do seem to suppress less but ultimately any steroid will cause you to go into a low testosterone state, unless you are using testosterone with your other steroids.
As far as androgen receptor competition read this thread;
I guess it’s possible to take such a high dose that there are no longer any open androgen receptors but you have to remember that 50mgs of anavar a day doesn’t mean all 50mgs is all of a sudden in your blood and trying to find a receptor. I think anavars half life is 9 hours so for the 9 hours after you take it 25mgs get broken down and used, it’s not all at once. So even on a high dose of multiple compounds there are always receptors that become free because the molecule that was attached has been broken down or used up. Then you can factor in the level of development for the person, I don’t think you can necessarily grow new receptors but I believe they do become more efficient at processing the compound that attaches. I have read that we can grow new receptors but I don’t think that sounds correct, I think we can stimulate receptors that were previously un stimulated.
Now steroids are unusual in the sense that 1 plus 1 does not equal 2, it actually equals 3. There just a magnifying effect when you combine two or three different compounds. So that is a big reason why people stack. I personally have found out that when I use two DHTs my fat burning goes through the roof even if I am not eating the best food.