I wouldn't say you'd need a top shelf receiver, but a 55w Onkyo probably won't like driving these guys (what model?). It isn't simply the wattage, but how well the receiver's power supply reacts to the low impedance load. That is not to say you'd need a $1000 receiver to drive them, but something that has a decent power supply. If you are stuck with the receiver you have, I'd probably look for something else. -3dB @ 65Hz means they won't have a ton of bass without a sub, but they should do OK.
Mordaunt Short 902s are $199/pr
here (they may still have free shipping too) and will have a similar "British" sound to them as the EPOS. They are -3dB at 55Hz and are 8 Ohm. I'm quite happy with them for music.
Next choice might be the Onyx X-LS or the new HSU HB-1.