I've been a BAT man for about 5 years now. I upgraded to a BAT VK-90 last year and was amazed at the improvement of space between instruments and the air around vocals. BAT is an outstanding brand of product, as is the company and people there. I really don't think I will change to another brand, but I am likely to continue to upgrade within the BAT line of products.
To the question of the OP, transformational products for my systems, over the years, have been phono cartridges and phono stages, speakers, and most recently the BAT VK-90 preamp. What a fun and pleasurable journey it has been.