thats the problem here with you and a majority of this forum. you dont HAVE to feed a sub over RMS in order to get everything out of a sub. Why throw more power at something (spend more money) when you can build a box thats going to give the absolute most (less money).
I'm helping the OP in the way, that some dudes telling him something thats not necessarily true to his situation. Your e8's Don't (need) more power, furthermore lets say those e8s are getting 400rms each, which i would hope your amp has no issue giving you given the correct box they should be more then enough.
I'll ALWAY'S recommend box over recommending more power.
Plus it seems like you cannot fathom how a gain pot works. Those numbers on your amp are a generaliztion of where it might by, on some amps youd be real surprised how far off that pot could be.
Maybe buy yourself some tools (IMSG, DD1, CC1) therefore you can take the guess work out of those tunings, and you can give the op a more educated response as to how he can better the situation.
For the op.
Since you already have the equipment, i'd use what you have, and just hope that your box guy is familiar with the power you will be giving them and the vehicle arrangement that they will be used in. Answering your question directly is very hard since we do not know what voice coil configuration that you have or even the electrical your vehicle has in order to sustain the output of a potential 2k rms system.