HE4THEN
Thanks for the reply. I've done a bit of searching for a suitable amplifier but could not really say what is the proper one for such a scenario (NU Audio Pro -> Amp -> JBL Control 5 + sub.) Does it affect or do I lose any benefits of the card and sound quality going from the card into an amplifier and then going to the speakers (absolute greenhorn when it comes to audio)? Would it be be better to just go directly into some active speakers such as the Presonus Eris E5 for example? Though I'd really prefer to use the Control 5's with a sub to be honest.
No prob, I have spend a lot of time lately researching for different audio solutions, it really takes time to begin understand those things.
Your monitors are closer to classical HI-FI system in this regard. You need external sound source (your PC in this case), that will convert digital data to analogue, amplifier, that will amplify the analogue signal and by doing so - drive the speakers in your acoustic. There may be additional physical items like EQ, pre-amp and so on, but rly you don't need that. You do need amplifier cause the sound card can't provide enough current to move the speaker heads (fast or at all). Too heavy for it.
The amplifier needs to put in as small distortion as possible, while providing enough current to move the drivers and return resistance to provide electric dampening (sorry if I miss proper English terms). You can dive into the details if you wish.
Good amplifier won't spoil your sound in any way, its a must-have component. You will have no sound at all without it.
So, check for any pro studio amplifier or home hi-fi stereo amplifier that can receive the analog signal by RCA/Jack cables and pass it by acoustic wires to the speaker system. You don't need digital input (it would mostly deny the purpose of the sound card, since its DAC won't be used and you'll buy a subsystem that you already have). Also, don't go for receivers (for home cinema) unless you plan on 5.1/7.1. Don't search for one with digital sound corrections or some other sophisticated features, your PC will do better.
Also, subwoofers are usually active anyway, if you'll wish one. Don't need amp for that.
Active speakers are simply passive speakers + onboard amplifier. There are differences (active crossover put before amplification, bi-amplified system), but its not crucial. If you like the sound of yours, then there's no problem.
By the way, have you used the JBL Kontrol 5 before? How were they connected?
P.S. While I am at it, you'll also need acoustic cables. There are different types of scam with cables. You really only need thick copper ones. May be you'll need cables with isolation, if there is noise. The silver plated cables made of 99,99% pure copper are just a scam, don't get caught.