Um, you should definitely return that Sound Blaster card. Your Asus P8P67 motherboard has better onboard audio than that card! You're truly getting no value at all out of that Sound Blaster X-Fi Xtreme Audio card. Good thing you can return it and get your money back!
So yeah, your P8P67 motherboard definitely has an optical digital audio output. And frankly, it's got pretty darn good built-in analogue audio support as well. So you can go either way with your speaker setup and feel good about just using the audio that's included with that motherboard
So yes, as mentioned before, if you truly only care about using your computer as your only source, you can just get a powered subwoofer and a pair of powered speakers. Use the analogue outputs from your P8P67 motherboard, and you're all set! No external DAC or AV Receiver needed.
If you think there's ANY chance of ever wanting to add another source though - such as a game console, DVR, Roku box...anything - then having an AV Receiver like the $99 Onkyo HT-RC330 will come in very handy
And you can use the optical digital audio output from your P8P67 motherboard. No muss, no fuss. Easy
It's rare to find nearfield monitors - self-powered or passive - that come with speaker grills. So if having speaker grills is important to you, it's probably easiest if you go with using the optical digital output on your P8P67 motherboard, run an optical cable to the $99 Onkyo HT-RC330, and connect that Onkyo AV Receiver to a subwoofer and a regular pair of speakers.
I'll be perfectly honest, the only reason I didn't recommend the Energy S10.3 subwoofer that is less expensive than the HSU STF-1 is because I haven't tested it for myself
But I trust the other helpful folks here, and the reviews and measurements do look good! So I've zero problem with that Energy subwoofer as a slightly less expensive alternative to the HSU STF-1 that I recommended. I just like to stick to recommending products that I know I can vouch for because I've heard them in person. But I haven't heard everything!
So yeah, that Energy S10.3 looks like a great alternative that can save you a bit of money vs. the STF-1, and give you a little extra room in the budget for speakers!
Speaking of which, you've got roughly $250 in the budget for a good pair of speakers if you go with the Onkyo HT-RC330 AV Receiver and Energy S10.3 subwoofer. Anyone who knows me knows that I'm a huge fan of the
Ascend HTM-200 SE speakers, but they'd be a good $50 over your budget.
One of the main reasons I like both the Ascend HTM-200 SE and the Behringer 2030P so much is because they both blend really well with a subwoofer, even in a small, nearfield setup. That's a lot tougher to accomplish than you might imagine. When you're listening nearfield, it starts to get really easy to hear the subwoofer as being a separate speaker from your main pair if you're forced to cross the speakers over to the subwoofer at a higher frequency than 80 or 90Hz.
Ideally, you should never really notice the subwoofer as being its own, separate speaker. It should just seamlessly blend with the main pair so that it seems as though you just have big, full range speakers sitting on your desk! It's a great illusion when it works, but it sticks out like a sore thumb when it doesn't. So I do not take that blend between the subwoofer and the speakers lightly! It's probably the toughest and most important thing to get right in a nearfield setup.
So, to give you an option that will keep you well within your budget, I'm going to do that thing I hate doing and recommend some speakers I haven't actually heard for myself yet. But I'm putting my faith in the designer of these speakers and basing my recommendation on the previous line of speakers that he designed for Pioneer.
The
Pioneer SP-BS22-LR - $130/pair
I must say, I'm really not a fan of using rear ported speakers for a computer desk setup. So I hope you're somehow able to position either your desk or these speakers so that they have a good amount of distance - at least 1.5 feet, and hopefully more like 3 feet or greater - from the back of the speakers to the wall. But if you're not able to do that, you can maybe use a couple of
absorption panel bass traps on the wall behind the speakers to mitigate any strong reflections or noise coming from the rear port. With the low price of these Pioneer speakers, you can afford a couple of 24" x 24" x 4" bass traps, or even less expensive would be a single 48" length bass trap hung horizontally on the wall behind the speakers
Acoustimac's bass traps are inexpensive and work well, and they even come in suede or printed patterns if you like! I'm always a fan of getting some acoustic treatments into any room, so this might actually be the most "complete" solution all around.
So yeah, that's pretty darn good looking to me!
Return the Sound Blaster X-Fi Xtreme Audio card
Use the optical output on your Asus P8P67 motherboard.
Connect an optical digital audio cable to...
Onkyo HT-RC330 AV Receiver
Energy S10.3 subwoofer
Pioneer SP-BS22-LR bookshelf speakers
with one or more 4" thick...
Acoustimac bass trap(s) in plain fabric, suede or printed pattern on the wall behind the speakers.
That's pretty fabulous actually! And all within your $600 budget!