Grafkin . . . fyi, I checked the specs for each of these:
the Klipsch HD Theater 600 5.1 package for $300
Monoprice 5.1 Theater Package for $250
The Monoprice 5.1 specs are better than the Klipsch for $50 less! Here, look for yourself:
I know that how they sound is the bottom line . . . but NO budget package is going to be audiophile approved, ever. Yet, looking at the specs on the Klipsch compared to the Monoprice set, well, I'd jump on them in your situation. Even after shipping you'll only spend around $290, well within your budget.
I've yet to be disappointed with a monoprice item based on bang for buck. Look over the reviews and make an informed decision.
Here's some more info to consider . . . while some of the Kilsch speakers are wonderful, I don't think this particular speaker package is worth it . . . especially when the frequency response on the Kilpsch is only 150 hz - 20 khz. The sub is 33 to 200 hz.
This means the Klipsch speaker midtones (voices in music and video) are weak, and the high sounds can (will) be overbearing, meaning that the subwoofer is going to be doing ALL the midtone and low end sound. This is NOT good. The subwoofer should do the lower end stuff, like 80 hz and below. The sub is not (necessarily) designed to do the midtone sound, which means ultimately this speaker package as a whole will have, dare I say it, higher tin-like sound. But this is just a guess, based on the specs. The might sound great, but based on the specs, I'd really want to audition them before purchasing them!
The Monoprice specs are 110 hz to 20 khz. Not much different than the Kilsch, but definitely better! At least these speakers have some midtone ability, the Klipsch do not. The Monoprice sub is 30-150 hz, which is a tiny bit better then the Klipsch sub. Like the Klipsch, the Monoprice sub will handle some midtone and all the lower tones, but not nearly as much as the Klipsch. In my would, that means the monoprice speaker package is much better, spec per spec, and price for price.
Ultimately, of course the quality of sound is all that matters . . . but for a budget package system for under $300 which includes shipping, and the reviews of the Monoprice 5.1 speakers seem reasonably good, I'd seriously consider this product.
Lastly, like I have already said, some Klipsch speakers are quite nice, I just don't think this particular package is as nice as some of their other speakers (which cost so much more).
Oh, real last thing . . . if you can find (on ebay, craig's list, etc.) the older Yamaha NS-P436 package, that would be better than anything listed above. The have much better specs than the monoprice or kilpsch packages for only around $200! And this speaker package will work very nicely with your current older HTR Yamaha. I have used this package on an older HTR system like yours, and they do a wonderful job; 70 hz - 60 khz on satellites speakers, and 30-200 hz on the sub. The have a nice clear smooth midtone range for voices. All in all, they sound nice, especially for the budgetary conscious!
Good luck . . . don't get hung up on Big Box Store brand names or black friday (imaginary) super deals . . . there are other speaker packages out there with better specs from a number of speaker manufactures that are within your budget.
And hey . . . I do not work for Monoprice or Yamaha! . . . FYI . . . I also have Polk Audio speakers, too. I look for a balance between good specs, price, and sound, and all of this is arguable! So let YOUR ears decide.
Good luck! I'd be interested in knowing what you decided to purchase . . . no stress, LOL!