Passive Bookshelf speakers Amp suggestion.

Magnat Edelstein is no cheap speakers.
You should go for good amps.

Yes, if I am not mistaken, Creative ZXR soundcard is more aimed for the headphone end amplifier not for driving speakers.
However, it should have also outputs (RCA) for the normal PC active speakers, you can use this to connect to the amplifier.
So, you do not have to throw your soundcard away, especially if you still plan to use a headphone (over 32 Ohm)
But, if you are not planing to use headphones anymore, yup, you can simply sell this soundcard.

How much is your budget? Regardless of what you wanna do with the soundcard.
If you are quite low on budget, I would recommend Denon PMA 520 or 720.
It should be about max €250.

FX Audio D802 2x80W 192KHz Digital Remote Power Amplifier ($110), or Audio Source AMP100VS 2 Channel Amplifier ($132), or Dayton Audio DTA-120 Class T Digital Mini Amplifier 60 WPC ($105, headphone output also), SMSL Q5 Pro ($140), Topping TP-60 TP60 2*80W High Power Class-T AMP TA2022 Stereo Power Amplifier($200).

I was unable to find a price for the magnat m600, but if it's one of the more expensive dac/amp combos ($500 and up lets say), there are plenty of options available as well. You could, say, use a Emotiva BASX PT-100 Stereo Preamp/DAC/Tuner, in conjunction with an amp. A good option to consider might be to look in your local area for a vintage receiver in acceptable condition. You never know, you might luck out and find something awesome on the cheap that sounds better than a lot of far higher priced options.

You could also look into getting a newer integrated amp from Marantz or Denon, or Yamaha, Onkyo, etc. Another option is to add those speakers of yours to a 5.1 setup. Dayton Audio offers an excellent pair of floorstanding speakers (Dayton Audio T652 Dual 6-1/2" 2-Way Tower Speaker Pair, $118), and add a subwoofer as well, from dayton for another $100. A 5.1 receiver with the wattage your looking for can be found for as little as ~$150. Bic also makes some excellent subwoofers and speakers.

Your sound card isn't bad, though tbh some of the latest z270 motherboards are offering much of what you'll find on it, onboard in their audio codecs. But your soundcard is fine. It really depends on your budget and quality of sound you want. If you have a flac library, I'd suggest an endgame of finding a quality DAC and AMP. Though for now any of the above solutions should suit you fine. Heck, you'd do ok with a Nobsound® TPA3116D2 Mini Digital Amplifier HiFi 2.1CH Stereo Amp with Power Supply, gives you the option of adding a subwoofer in the future and only $75.00.