It is perfectly normal that Kramer don't quote a distortion figure for this switcher: it is a mere mechanical switch, so it effectively doesn't add distortion. As for the other one, the distortion is caused by a passive isolation transformer, not by the switch itself. It is therefore not quite transparent, but it would be a mistake to believe that this .2% THD will ruin the signal, actually it is not at all like semiconductor-generated distortion - quite a lot of (reputable) engineers swear by this property of transformers to "improve" the sound, and would not touch a transformerless mic pre with a 10-foot pole. Also, note that the transformer is there to prevent ground loops (ie. mains hum), and it thus avoids problems in quite a few situations, although hopefully not in your case.
Now for your problem: analogaudio is perfectly right, a Y cable is good to distribute one output to two inputs, but using one for output sharing is begging for trouble. If you want to share outputs, your best option is either a mechanical switcher (Kramer is a decent broadcast equipment manufacturer), or a patch bay which is just a professional way to rewire more conveniently, all passive, nothing more than 2 connectors and a few cm of cable.
Example of decent patch bay at a reasonable cost: http://www.neutrik.com/en/products/audio/patch-panels/1/4-patch-panel/nys-spp-l1
Example of simplified patch bay (actually a mere panel with XLR connectors that you have to solder yourself): http://www.xlrpatchpanels.com/
Ok, the patch bay is a bit more cumbersome to use, does not look as sexy as "audiophile" stuff, but it is hard to beat in terms of simplicity, quality and reliability. Look at what the studios use, think that all
your records were recorded through it, and see if you can live with the looks of it - WAF can be a problem, that would be the most relevant objection I reckon
Also, it is not clear to me whether you want to mix balanced and unbalanced signals. If so, adapters are necessary to match the levels, and it is much easier to convert balanced to unbalanced than the other way round.