Hope i won't confuse the matter even more....This is what i do when i'm not climbing trees (set up sound systems that is, not talk crap on here).
firstly you need to look at the numbers together.
8 ohms impedence - this is the resistance.
400w PGM (program, or 'RMS') - this is the power. (ignore 'max' ratings)
you will need an amp that is rated at least 400w rms per channel at 8 ohms.
ideally, without going much into the details, you need to put around 1.5 times the rated power into the speaker - so, 600w rms @ 8 0hms into each speaker. underpowering the speaker will pose a greater risk than overpowering.
now, looking at that amp on ebay. it states "2 x 400W max. at 8 ohms" which in real wattage is around 150-200w per channel. this will underpower your speakers by 50-75%
and the power rating isn't everything - the sound quality will be pants - you certainly won't get deep bass, clear mids and sparkling high's from that chinese ebay thing.
for around £100 you will be better off buying a good, second hand amp.
something like this behringer amp would be good - this is a make that specializes in the lower end of the pro market. it has around 550w rms per channel at 8 ohms
BEHRINGER EP2500 Power Amp. on eBay (end time 07-Feb-10 20:07:33 GMT)
some other makes to look out for that will be within your price range are crest, carlsbro, qsc, matrix, peavey, ecler, old crown's, inter-m, c-audio, t-amp, warrior & yamaha
plus the leads you will need....
a double phono to male xlr like this one to connect to a cd player .....
Cable - Double RCA Phono to XLR 3-Pin Male Lead (1.5M) on eBay (end time 12-Feb-10 22:17:26 GMT)
a 3.5mm stereo headphone jack to double male xlr, to connect to an ipod/mp3 player. like this...
http://cgi.ebay.co.uk/HQ-3-5mm-Stereo-Jack-Plug-2-x-XLR-Male-3m-Length_W0QQitemZ200370790524QQcmdZViewItemQQptZUK_Computing_CablesConnectors_RL?hash=item2ea707a07c
and finally, two speakon to speakon lead to connect the amp and speakers.....
http://cgi.ebay.co.uk/Neutrik-NL2FC-Speakon-Speaker-Cable-Lead-1m_W0QQitemZ320468151110QQcmdZViewItemQQptZUK_Computing_CablesConnectors_RL?hash=item4a9d63eb46
hope that's helped - let me know if you need any more help