With all due respect to those who are so minded to modify their multi-effects pedals, I suggest that before you tinker with the hardware of your gadget to solve it's "thin" or "nasal" sound, I think it would be better for you to try out some of those patches readily available in the internet and tweak them, keeping in mind the sound you are aiming for. The drive effects of all multi-effects pedals have a wide range of sound color that it's easy to get confused and get tangled in a loop of sound ideas. If you will listen to all the modules in the effects chain of a pedal, most of the effects have tone-altering parameter or components. You have to distinguish carefully how each effect changes the sound and how it's making it closer to the sound you want. For example, short delay chorus introduces some odd harmonics and has the effect of damping low and middle tones. Also, higher gain is often perceived as higher in tone.
It is also a good practice to get a good stock guitar-amplifier sound first before tweaking your multi-effects. The idea is to get good compromise between the guitar and amplifier tone output as close as possible to the your ideal sound then work your multi-effects from there.
It is misleading to say that a hardware modification in your multi-effects pedal will solve your tone problems. Hardware modifications do change the sound of gadgets but bear in mind that a stage in the gadget can never exceed the operating range it was designed for. There are compromises in modifying a device. Most of these modifications are introduced only in the analog part of the circuitry and will most likely affect only the gain and/or tone/frequency response of the stage being modified. Very often, increasing the limit of one signal character, gain or tone, will decrease another signal character. An alternative non-invasive way, which I think is better, is to adjust the gain and/or tone response of the stages in the effects chain.
Don't you think that if the simple issue of having a "thin" or "nasal" sound has been around from the time Zoom came into being, the designers at Zoom would have solved it by adding or removing a couple of cheap components? If the smart mod guys here in philmusic can find modification designs, schemes and diagrams in the internet, why can't the people at Zoom find them? Are they really that stupid and dense? Pedals/Effects modification diagrams are all around the internet (google is your friend).
I think, the bad reputation that Zoom has been attributed for is largely because of the default patches of their effects. But, like all default patches, they are designed to be demonstration patches to underscore the sound/tone idea associated with the patch. You may say that the Zoom sound is their trademark. After all, the multi-effects you have has passed through many research and development stages to give the best compromise between what the whole device is capable of and the whole range of guitars and amplifiers it will work in.
If you have a bad or mediocre guitar or amplifier, you will not get very far in getting that elusive sound that is in your mind. At most, a bad or mediocre guitar or amplifier can sound good, or a good guitar or amplifier can sound better with a multi-effects pedal. If you're looking for a patch that will make your Fernando (no offense to Fernando owners) sound like a PRS, you can tweak our pedal to death and you might get lucky but don't get your hopes up. It's like applying a car wax to make your Kia look like a BMW. But in the end, after a hard day's work, a Kia is still a Kia and a BMW is a BMW but you can always say to your self that your car shines like a BMW, even though it doesn't look or feel like one.
The point here is: be patient, be smart, be creative and take pride in your work.
But if you have already set your heart and mind in getting your pedal modified, then go ahead. There's no point in using something you are not comfortable or satisfied with. Good luck.