I bet you any switch under several hundred dollars will be much the same. If you are using one as a composite to Svideo converter you are going to get bad results nearly every time. Many of them don't even send the composite signal ins through their Svideo outs. You plug in composite, they will only output composite.
Plan A:
I suggest you use an external amp (which I assume you are already), and buy a good quality 5-6 Svideo box and put it into video 1 on your amp. Use the one you have already for your composite signals and put it into video 2. Most amps are going to be 2 times better converting your composite signals to Svideo...unless your amp is cheap. If it is. Then route video 1 into 1 of your TV's inputs. And route video 2 into a 2nd input on your TV, but keep the video 2 line all composite.
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Plan B: Buy a DVD to VHS copy box for about 20 dollars. This is basically a tiny chip based amp with a chip based signal limiter on it. It will probably make your 1 thing which looks fuzzy, look fine. I'm still a fan of plan A more though because it is the correct thing to do, on the cheap. Plan B is psychotically cheap but may or may not work.
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Plan C: Buy a 10 channel video mixer. It's really what you need if you want to be picky. Then you can set the "volume" of each video and audio channel to make each one perfect.