I don't get it.
Why put a Mic pre into the the Eventide? What about phantom power and if the mic pre fails then the the Eventide fails.
In my experience you cannot build a "decent" pre that small. I highly recommend you go out and buy a decent pre amp. Also if you spend anything less thatn US$1000 on a pre then you have proberbly bough one whose sound does not do justice to your signal path and you will be feeding sub-standard sound to the Eventide.
Personally I spent some time trying out various options and have invseted in a serious signal path. The reason being if I record synths, samples, vocals, guitars and anything else it will sound good.
The pre-amps i landed up getting are Great River ME-1NV's as I like their sound and I can also use them when mixing by running my master buss out into them to add some color/flavor if you like. They rest of the chain is a Great River MAQ-2NV Mastering EQ and a SPL Kultube with Luhndahl Transformers. This chain gets used for mastering as well with my H8000 as well.
So the mastering chain looks like this;
ME-1NV -> MAQ-2NV – > Kultube -> H8000 = Classy.
Also another reason you would not want to build a pre-amp into the Eventide is to add other processing to the chain before it reaching the Eventide like a bit of analog compression. Another thing to consider is you will devalue your unit quicker rather than add value by doing some obscure non stardard modification to you unit.