Well, the simplest thing to do is to update to 3.7.1 Launcher.dat and then update your EmuNAND to 11.0 and keep using it as you have always done so.
Now if you want A9LH, avoid GW-A9LH at all costs, it's a locked down version that keeps you completely locked down to Gateway3DS, you won't have access to recovery tools like EmuNAND9, Decrypt9, Hourglass9 or options to use other CFW like Luma3DS and others.
Now with that said, I'd recommend you look at this guide.
Link: https://github.com/Plailect/Guide/wiki
Plailect's A9LH Guide will get you fully setup with Standard A9LH, with Luma3DS as the CFW choice for your SysNAND. Once you have A9LH fully setup, you can then follow this guide I wrote to basically dual-boot Gateway with Luma3DS.
Link: http://gbatemp.net/threads/431691/
If you still have any further questions, don't be afraid to ask~
Is there any benefit to using A9LH over Gateway w/ Emunand? Ideally, I'd like to be able to just power on my NN3DS and have it on the latest Firmware and be able to run homebrew and whatnot. Right now, I have to use Zelda OOT3D to boot into Emunand meaning I need to carry my Gateway Red card, and Zelda just in case my NN3DS powers down. Am I correct in believing that the A9LH method will do that? Is there any way to convert my Gateway Emunand to be used with A9LH + CFW? I found THIS thread which sounds exactly like what I need to do. It should be fairly similar, right? Only difference is he has O3DS and I'm using a NN3DS.