Can you buy Mirage speakers where you live? I had the exact same issue your having now, as I was looking for a decent speaker system for my somewhat large Master Bedroom, yet limited access to large speakers. I tried several different brands before finally deciding on the Mirage Omnisat Micro's
Also if your open to shopping on ebay, I see them all the time for around $90 per speaker, and this is half price since their discontinued. Don't confuse them with the "Nanosats" that are the new model. The Mirage Omnisat Micro's go deeper as their mid/bass driver is a little larger. I couldnt believe my ears when I first heard these little guys, and since they use omnidirectional sound technology, not only does the sound stage sound excellent, but to see that it's coming from these little speakers will blow you away! They are very non directional, hence its very hard to locate where the sound is coming from (much like a subwoofer's phylosophy with low frequencies).
I found a great deal on a Velodyne 1200 watt sealed enclosure sub with an 8" driver that will reach up high enough to meet where the Omnisats start to roll off. And the Velodyne will reach all the way down to around 28Hz with power to boot! So with all this being said, I'd look around for a Velodyne Sub (you can find them for around $300 american dollars) with an 8" driver that can mate with decent sattelite speakers such as the Mirage Omnisat Micros which can be found for $500 for all 5 speakers. And, if you ever decide to go to 6 or 7.1, you can buy an additional Omnisat Micro by the speaker (doesn't have to be purchased in pairs).
If you can get these in Europe, I'd highly suggest buying them while their still around! If you were considering Bose, or Sony at the beginning of your search, this system will blow away both. Not even in the same class of speakers period.
For another suggestion, I agree with Tony (i think thats who recommended these) and consider the SVS SBS-01 speaker system. I've ordered and installed two of these systems for friends of mine, and they too are nothing short of fantastic! A little pricier than the Mirage/Velodyne system I recommended, but worth the $$!
Let me know if you have any questions about either of these systems and I'll provide more specific links.
For the SVS - SBS-01 System you're looking at $1000 american dollars
For the Mirage/Velodyne system you're looking at around $800 american dollars (sorry dont have a money conversion chart handy)
Both of these systems will sound great with your new Onkyo!