New sound setup for my PC

Any receiver with a digital input includes the DAC you need to work with the digital out in your computer. For example, even the bottom of the line Denon AVR-1312 has at least one digital coaxial input (as well as one TOSLINK); and you should be able to find something similar from your favorite receiver vendor. However, do check the specs for the DAC in the receiver just to confirm that it will accept a 96 kHz/24 bit data stream (which is not coincidentally the maximum that a DVD-A delivers). Finally, confirm that your software player can direct audio to the digital out. In terms of power output, I am not sure about the ideal receiver for the Nubert nuBox 381s. You might try posting to AVS Forums for suggestions. Sorry I can't be of greater assistance in that regard.

One feature that you may want to consider when looking for that receiver is either a pre out or a tape monitor - either could feed a headphone amp . . . should you be so inclined.

The Onkyo receiver line can be surprisingly hard to find on their web site. I knew they were there, and it still took me a minute to find it. Not that the A-5VL isn't great; it is a more traditional stereo receiver that excludes the video stream. I like the versatility of an AV receiver as the older units can move from the living room to other rooms in the house as I upgrade. This way console gaming, watching movies or listening to music are activities that are not confined to just that one room. This may or may not appeal to you; and is just another option to consider. Speaking of which, I am assuming that you have no interest in separates - dedicated DAC, pre-amp (or headphone amp) and amp.

As to brand. I've owned Sony, Pioneer and Onkyo (current favorite). My opinion is that Denon and Onkyo are better values than the alternatives; but my opinion is based on features and specs - not actual SQ as I couldn't possibly hope to A/B my way through even a handful of AVRs. Home theater and stereo magazines help, but I often feel that they are just this side of "better than nothing"; as, in the end, your room, speakers and ears probably do make your perception of SQ unique.

As to how to distribute you funds. Spend as little as possible on the receiver, and spend as much as possible on the speakers. Build a short list of speakers to audition (the magazines can help with this), and see what you can demo in circumstances that match your home as closely as possible. Unfortunately, at our price points, this probably means buying from a source with a liberal return/exchange policy or playing around with used equipment.

I should have thought to ask earlier . . . are you primarily interested in listening in front of a computer screen? If that is the case, then near field monitors (studio monitors) might be the better choice. However, you will need the desk space (or space at the sides of your desk for speaker stands) and an unobstructed line-of-sight from the speakers to your head (you are going to aim them right at your head); and the listening sweet spot is going to be a space just a little bigger than the size of your head. If studio monitors interests you, then the optimal audio chain is pretty much what you would want for your headphones:

Computer > DAC > pre-amp (or headphone amp with line level outs) > headphones/speakers. The problem can be volume control for the speakers (which is why a pre-amp might be a better idea). There was a fairly recent thread here on Head-Fi that might be helpful if this sort of speaker interests you.

I agree . . . no point paying for features you don't need. I think you have done all you can short of getting to listen to your choices together in a store.

Just saw your edit to the original post. I never know how to take nominal impedance: it could be an estimate of actual current draw, or it could an attempt to make the speakers seem more "high end". Yes. I am that cynical when it comes to speakers and nominal impedance. As long as you are listening at moderate volumes you should be fine - at least in my experience. I have an old thread bookmarked that may be helpful in this regard. However, if you are the sort to run your stereo with the volume cranked to ear splitting levels for hours on end, then you may want a more robust amp.

I'll look forward to hearing your thoughts when the goods arrive. Exciting times!

Great! Glad you are happy with the results. Unless you really want to, I wouldn't worry about deciding which you prefer - your speakers or your headphones - just enjoy the music.