I'm not a basshead, but I bought Castor Bass out of curiosity. Way too bassy for me.
Yesterday I replaced the stock nozzle silver filter with a 5mm 500 filter. The transparent area is much bigger in the 500 filter.
Filters held up against a window:
Stock filter to the right. (It's silver, but looks black due to the backlight.)
I must say they sound amazing now. Great extension but never sibilant. Still very bassy, but it's not bloated. I'm using them as my "fun set" for hip hop and edm.
Setting 0011 and using Tang Sancai balanced tips.