the way i have it is, sound card L&R out into 3.5mm jack spliter, so effectively I have two 3.5mm female jacks for my L&R sound out, I use one jack for my logitech speakers for gaming and generale music listening,
the other jack I connect a 3.5mm jack to L&R phono up to my mixer into any of your channels , I have my monitors plugged in my mixer using the balanced tsr/xlr outputs. Your decks are plugged into your mixer right?,
then output the rec out of your mixer to the line in on your sound card, I myelf have done it like this, I also have the master L&R phono out of my mixer plugged into my hi-fi stack so I can get a good idea of what it will sound like through a hi-fi and also it's handy for thumping music out as we all know monitors are only really designed for just music reproduction,
this setup enables me to listen to my vst's and music software on my monitors from my pc througth the mixer, also it will enable you to listen to your decks throuth the monitors througth just the mixer or througth the mixer, througth the pc (for recording) then back out to the mixer to the monitors again, and,
if you want you can add a standerd set of pc speakers to the secound 3.5mm jack like I have so then you can just switch off your mixer and switch on your gaming speakers for sourround sound gaming, (if you are going to use a 5.1 speaker setup then you can have the L&R rear and C&SUB jacks coming straight from the sound card to your speakers, its only the front L&R that have to be routed from the spliter, this is so I don't have to use my mixer all the time to listen to the pc, lol
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this setup may not work for you as it all depends on your personal needs, setups can be very unique to each user.