I'd suggest you don't get the Visivox. You need two mono preamps like that one to record in stereo.
Sony mics tend to be made for Sony recorders. I've had a few of each. Your Sony mic has a 1/8" stereo plug, which may limit your choices, unless you're comfortable recording in the wilds with seven inches of adapters hanging off a two inch MP3 recorder. To avoid adapters, I've tended to solder my own plugs on cords when I have a portable recording rig.
I've never seen a semi-pro mic preamp with a 1/8" stereo mic input. They tend to have 1/4" (unbalanced) plugs or 3-pin amphenol (balanced) connectors. I can't tell what kind of input jack is on the Cowon, or if it has the ability to control input level.
If the Cowon doesn't have recording or input level adjustment, then somewhere between mic and recorder you need a control that lets you change the volume of each input signal. Instead of buying a pair of preamps, You may wish to buy a mixer with built-in preamps. When my kids aren't climbing all over me I'll look up a few examples.