complete noob here---why/how can speakers be considered too big for a particular room?

I welcome someone to prove me wrong but other than not fitting: they can't be too big for the room.

Back in the 50s-70s, there were some horn-loaded speakers where the speaker was an add-on to the house and the cone mouths filled the wall of the room.

Speakers can be larger than one needs for the room size, but that's not the same as being too big. And speakers can have too narrow a dispersion angle to work well in a short room, but the dispersion angle and size aren't necessarily directly related. No.

I think recommendations you get from AVS members will be better than Logitech PC speakers, even their 5.1 setups. The best 2.0 PC speakers I've owned that were specifically made for small desk PC locations were the Creative GigaWorks T40. I used these in a 2nd PC location but used a pair of AR Powered Partner 570's with my main PC on a 30" x 60" desk with 30" monitor. I've had the 570's for 18 years and haven't found anything to match them in the $300 range. The T40's sound like cell phone audio compared to the 570's but, after 18 years, I'm looking at the Emotiva Pro Airmotiv 5's to replace them. Emotiva has three powered monitors, the Airmotiv 4, 5, and 6 with 4.5" / 50w RMS, 5.25" 100w RMS, and 6.5" 210w RMS respectively. I believe the sale prices now are $350, $400, and $580. The 5's have a 7.5" x 8.5" footprint, which is slightly larger than the 570's. Audioengine sells two powered monitors, the a2 and a5 with 2.75" / 30w RMS and 5" / 100w RMS respectively. Retail price for these are $200 and $400. Emotiva uses folded ribbon tweeters vs. silk dome for Audioengine. The a2 is tiny ( 4" x 5.25" footprint ) and the a5+ is about the same size as the Airmotiv 5. The Airmotiv are traditional studio monitors with only RCA and XLR inputs and independent volume controls. You'll need a $4 RadioShack 3.5mm to stereo RCA splitter and a standard stereo RCA cable to connect them to a PC. The Audioengine are a more traditional PC speaker and have a 3.5mm input jack on one speaker. One speaker holds the amp and the other is passive. Speaker wire runs from active to passive monitor.

I just gave you a couple of powered options that should fit ON your desk. There are tons of options if you go non-powered with external amp/DAC and put them on stands/shelves. The Polk Monitor 30 II, 35B, 40 II, or 45B are excellent choices for PC audio. I think they are $200 a pair tops for those. Definitive Technology SM350/450 are good choices as well if you can find them at $200 and $300.

And... A note on speakers being " too big " for a room. My A/V room is 15' x 16' and I'm throwing an honest 2600 watts to 11 speakers not including the two 1800w powered subwoofers running at about 40% of peak. I don't think that is too much for my room, well, maybe a little.
Edited by jevans64 - 12/19/12 at 7:24pm

The way axis' of multi-way speakers interact can make some better suited for near-field (a couple of feet) listening than others.

I don't hear any difference between the majority of all DACs, and I don't think improvable error has been shown to exist in a normal, built-in DAC.

I think it's like tv's. You rarely hear people say "I wish I got that 42" instead of this 60" one".

Listen to some nearfield monitors, those intended for recording studios, placed as you will at home.

It's a massive leap from your current setup to what you were talking about, none of the gear you mention makes any sense to be honest if this is even remotely true: "for this first time venture as I'm not really trying to spend too much time nor money on my first setup." You should be looking at $4-600 a pair speakers.

And that Rega amp is a waste of money for your needs. Eg

http://shop.emotiva.com/collections/amplifiers/products/a100 or http://nadelectronics.com/products/hifi-amplifiers/C-316BEE-Stereo-Integrated-Amplifier is probably plenty

http://www.amazon.com/AudioSource-AMP-100-Stereo-Power-Amplifier/dp/B00026BQJ6 (10% of the cost of the Rega) is probably enough

http://shop.emotiva.com/collections/amplifiers/products/upa200 if it makes you happier

Or look at active speakers (amplifiers are built into the speakers) if you want to keep the clutter to a minimum:

http://www.avsforum.com/t/1440641/best-active-speakers-under-500

http://www.sweetwater.com/c405--Dynaudio--Active_Monitors
Are there any problems with the sound on your current setup? Humming, odd noises, etc? If not, focus on the speakers and their placement. There are plenty of DACs in the $75 to $150 range you can add later. Eg

http://www.crutchfield.com/p_773UDAC2B/NuForce-uDAC-2-Black.html
http://www.amazon.com/Audioengine-D1-Premium-24-Bit-DAC/dp/B006IPH5H2/
www.amazon.com/dp/B00A9LHLQ6

http://www.amazon.com/Behringer-UCA202-USB-Audio-Interface/dp/B000J0IIEQ if you want to try something
Edited by buzzy_ - 12/23/12 at 6:03pm

That's why you have to try them. No one can tell you what you like.