I wanted to do that. But it's impossible to downgrade a 3DS from 11.0 to 9.9 without HARDMOD. Soo, you gotta get your 3DS downgrade somehow.
His post says he's on 9.2.
I have a New 3DS XL on 9.2 and 11.0 Emunand with awesome IPS. Yes, I use menuhax.