The Triangle Titus XS is supposed to be a giant killer for right around $500/pair or just under. I haven't had the opportunity to hear a pair yet, though. I might just drop the cash to buy a pair based on what I've read. Trouble is, I'm not sure how to justify yet another pair of speakers...
I had a Triangle Titus XS once. My advise is to go listen to those speakers you are considering. Reviews are one thing. Actually listening to them is another. Each speaker impart their own characteristic to the sound. Some may like it. Some don't. Decide from there. System matching is also very important.
The Titus to me can be a bit bright. Or very bright if matched incorrectly. It was bright to me even when I was using a tube amp. And that amp is known to be on the warm side. If your source or amp is known to be bright, well you know what I'm getting. It images very well, very detailed. In fact the most detailed speaker I've heard so far so for those who's looking for that, you will not be disappointed. Bass is tight but doesn't go deep. If you have a subwoofer, I guess this wouldn't be a problem. Don't get me wrong. The Titus is a good speaker and it can do certain things other speakers can't match (at that price range). But like I said you have to audition it and see if the sound is to your liking.
If you are just starting out, my suggestion also happens to be the cheapest. Acoustic Energy Aegis One. It may not be as detailed or image as well as the Titus but I felt it had a more balanced and pleasing sound. Slightly more on the warm side but I'm slowly leaning towards the warm sound when it comes to a speaker system. A bright system and very detailed sound will only induce fatigue. It may sound great at first but over time you realise you can't listen to it for hours on end. My opinion anyway. Funny thing is when it comes to headphones, I actually prefer a bright sound. Go figure.
masz: What has to be taken into account is actually the place where the speakers should be set up. Because what can seem tob bright in the shop can just be right in an apartment full of stuff, heavy carpets & curtains, sofas... That shouldn't be forgotten.
The Triangles are great speakers but Masz is right about how bright they can be. Imaging is superb and the sound is very transparent. The lower end does suffer a bit though. Overall I think they're just a little bit too pricey.
The Acoustic Energy Aegis line of speakers are all fantastic for the price. From the Aegis one to Aegis three, all sound quite smooth and natural. In fact, I love the Aegis Three. I think it can be bought for a bit over $500 too (it's a floor stander though).
However, I would suggest a pair of the B&W 601s2. Good imaging, nice tonal balance and well detailed. The 601s2's are exciting speakers to listen to. Especially for bookshelfs. Bass is sufficient for a small room too. They're fast, dynamic and great for all types of music. But they have been criticized for adding coloration before. Some say it's just their distinctive sound. After auditioning every imaginable bookshelf, I settled on the 601s2's. They aren't absolutely perfect, but for under $500 USD I think they're fantastic.
I suppose your best bet is to go try them out and decide for yourself.
lini is right. The room also have an effect on the sound. However, with all things being equal, you can still gauge the general characteristics of a particular speaker. It would help greatly if you can outline the size of your room, how it is furnished, what kind of music you listen to and what sources and amps you are partnering it with. It will help in the decision process. No doubt some questions you may not be able to answer like your amp for e.g. (assuming you don't have one) but depending on the answer, a suitable recommendation can still be made. Sometimes, you don't know what you are looking for until you hear it so the best bet is still to audition the speakers. It may not match your room or source but by auditioning, you can at least get a hint if the sound is acceptable to you and you can proceed from there. No doubt things can get very expensive very fast. In that case I suggest heaphones! Can't beat them for value. But nothing beats a good speaker when it comes to soundstaging and bass.
Most entry level HiFi gel together quite well, stick to well know brands like B&W, mission, Kef and tannoy and you can't go far wrong. I got a pair of B&W 602S2 for £300 but you'll need stands for these. Actually you should put all bookshelve speakers on stands, they were not design to go on bookself in the first place. They work but to hear them at their best, stands are essential. Oh remmember to audition first!
If you have a limited budget and just starting out, my advise is not to spend too much. Even get secondhand. Tannoy, Acoustic Energy and B&W are all good brands. So are the amps that you've mentioned although I tend to lean towards NAD for value for money. The source (for me anyway) will only make a noticeable difference when you go higher up for the amps and speakers. Based on the music that you listen to, you will need a reasonable amount of bass. I can't think of any other speaker other than the Aegis (at a cheap pricepoint) which can give you reasonable bass without using a subwoofer. Supposedly it can go down to 38Hz although this is doubtful. It definitely has better bass extension compared to the Titus although not as tight. It is also easy to drive at 88.5db at 8ohm. Good for all-round music. Especially good for vocals.
For $500.00 here is a list of some different options:
Magnepan MMG 2-way Quassi-Ribbon/Planar-Magnetic speakers
Sound Dynamics RTS-5
PSB Image 3LR
Phase Technology PC 33
Paradigm Monitor 7
Monitor Audio Silver 3
Dynaudio Audience 40 $699.00 a pair