Owner manuals are a great place to learn about a product usually....
The "guitar" cables you have will work just fine, but you will need the proper adaptors to get into your soundcard. You will need a "stereo" (usually known and referred to as TRS (tip, ring, sleeve) connector on one end, and some sort of "mono" (usually known and referred to as TS (tip, sleeve) on the other end. In addition, this cable must "split" the signal at the TRS end to TWO TS ends. This is why it is referred to a "Y" cable, because it has one connector at one end, and two at the other end.
In this case, the TRS end has three connections:
Left Hot (usually the tip)
Right Hot (usually the ring)
Common Ground for Left and Right (ALWAYS the sleeve....)
Two seperate 2 wire cables hook up to this TRS connector so that you may have a "stereo" to "dual mono" connection from the soundcard. The Common Ground of both these cables obviously hook up to the "sleeve" of the TRS connector (sharing a ground is not a bad idea, and at some point, everything grounds to the same place anyway....)
"Y" adapters come in many connector configurations. If your soundcard requires a TRS Male (think of the anatomy!!!) "mini plug" (also known and referred to as a TT connector (tiny telephone) ) , you will need to find one that has that on the TRS end. The "dual mono" ends can be a number of different things, 1/4" TS, RCA, TS mini plug, even XRL. They can also be male or female.
In your case, you will probably want a TRS TT to Female 1/4" adapter. This may be hard to find! They are made, but this is sort of a specialty connection here, so they wouldn't be common. More than likely, you will find a TRS TT to Female RCA adaptor or TRS TT to Male RCA adapter. In either case, if you intend to use the 1/4" connectors on the cables you bought, you will need a further adapter if you have RCA on the mono ends of your "Y" cable.
These kinds of monitors, and professional gear in general don't usually have to adapt to soundcards that use TRS connections for outputs, so they don't provide the normal connections to get into them. Like with my soundcard (a Lynx One,
http://www.lynxstudio.com ) I have two XLR Line Level outputs, one for Left channel, and one for Right Channel. In this case, I would be able to plug those directly into the two inputs for you monitors. The 1/4" inputs on your monitors I will presume are for TS 1/4" cables. They MAY even accept a TRS 1/4" cable.
The difference between TS and TRS for a MONO cable is one is for a unbalanced connection (TS..only a hot and a ground lead...) and the other is for a balanced connection (TRS....TWO hot leads and a ground lead). The difference between balanced and unbalanced has to do with the OP amps on the units that are interconnecting. Some OP amps can accept balanced or unbalanced connections to them. Some can only accept one or the other. (back to the manual!!!). Whenever you see an XRL connection for a audio line, it will almost ALWAYS be a balanced connection (I as almost always because some gear may have been fitted with an XLR connection but don't use all three leads just so that the connectors are capatible with other gear without having different cable connectors on either end...but this is extremely rare...)
So, your monitor inputs (actually, they are power amp inputs....) would appear to be able to accept balanced and unbalanced signals. If you need to run long cable runs, balanced are much better for a variety of reasons. For short runs, unbalanced are just fine (and arguably better sounding according to some very noteworthy people in audio circles...verdict is still out though....).
We now have the issue of operating levels. Your XLR connectors make it so that your amps can run with a +4 operating level inputting to it. The device sending to the amp must be +4 for everything to jive well. Your 1/4" inputs MIGHT be able to accept +4 operating levels, but more than likely only accept -10 operating levels. Your SB Live card is most certainly a -10 output, so you will want to use your monitors 1/4" inputs from the soundcard. I won't go much deeper into operating levels. The only real thing you need to know about them is that the output of one device should be the same as the input of the device it is hooking up to. Feeding a +4 output to a -10 input would cause clipping and distortion at the input of the -10 device, while feeding a -10 output to a +4 input would mean that you will not get quite enough level to the +4 device for it to run optimimally. So, check your owners manual of your monitors and be sure of what the inputs to their power amps want to see on the various inputs.
Good luck.
Ed
