"or a pair of speakers: -- do you mean directly connected to the IPOD, like a docking station with speakers? If so -- forget about any good loud sound and bottom end.
Onkyo and Pioneer make decent stereo receivers. Unfortunately, the lower price of a two channel receiver does not include IPOD connectivity unless you buy an optional dock that connects to the receiver. These docks run about $130 and usually include the USB/video cable. Might as well look at a home theater receiver. not stereo. Home theater receivers play stereo also. As I tell people with buying a commputer or a receiver -- grow into it, not out of it.
I've seen the Onkyo TX-NR509 on sale as low $300 and the specs says it has a USB port for direct connect of an IPOD but you still need to buy the dock. Pioneer has the VSX-921-K for $399 which includes a built in dock and a cable. See the specs:
http://www.pioneerelectronics.com/PUSA/Home/AV-Receivers/Pioneer+Receivers/VSX-921-K
You didn't give any details about the size of the speakers you need. Bookshelf speakers and floor standing speakers have about the same freuency response at entry level prices. Frequency response of the speaker is what you have to look at. An average frequency response for entry level speakers is 49-20,000 Hz. The lower the first number the better the bass response. Floor standing speakers, though, could include 2 woofers (and the woofers in a tower can be bigger than bookshelf) as opposed to 1 in a bookshelf speaker and could give you better bass. Of course, you can increase the bass using the receiver and a tower speaker could better handle that. Towers, though, can be twice the price of bookshelf.
No matter what type of speaker, check the receiver power ratings -- don't exceed the max watts per channel that the speaker can handle. It's usually best to get speakers that can handle more than the receiver can put out so the speakers can handle music peaks better.
I am trying to decide whether I need a stereo unit or a pair of speakers to play music from my iPod and CD.
I need to play the low frequencies well (strong vibration) and loud. I'd like to ask the following questions:
1) Is it the stereo unit or the speakers that's going to make the difference (stronger vibration and volume)?
2) What numbers should I look at on the specifications to determine these qualities?
3) Any recommendations (or ones to avoid)?
Thanks a lot.

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