All this stuff is very good, and when you consider that the core system is £249 and extra units £99 each, the EOS system sounds like good value for money too. The one fly in the ointment is sound quality.
It's not that the EOS wireless system sounds bad. At low volume levels the output is clear, there's plenty of detail in the mid-range and at the top-end, and while the bass isn't particularly expansive, it is at least noticeably there. The sound is also surprisingly wide for such a small unit, SRS processing helping to produce a more immersive and less obviously directional noise than you might expect from such a compact unit. As a device for background listening in the kitchen while you're doing the washing up, either the base station or wireless speaker will do just fine.
All the same, there's not a lot of warmth to the tone, and the low-end and mid-range can sound thin, the bass in particular suffering from a general lack of oomph. This can make intimate, acoustic tracks, like Alison Krauss's Wouldn't be so Bad, sound cold, while rocky tracks, like Audioslave's Revelations, lose much of their impact.
Things do get better with a bit more volume, but you need to be careful. Just below half-way the sound rounds out and warms up a little, but push it further and the mid-range takes on a nasty brash quality, while the bass begins to muffle or even distort. The tight riffs and thumping bass of Revelations degenerate into a noise, while the loud brass passages in the funeral music from Wagner's Gotterdamerung are actually painful to listen to. In other words, the EOS is fine for background listening, but if you want to turn your music up loud and give it your full attention, this probably isn't for you.
There are some other points to consider here, however. Due to the back or floor firing design of the bass speaker, the performance depends a lot on what surface you have the base station or wireless unit sitting on. Wooden floors, thick kitchen worktops and nearby walls are fine, while chipboard shelves or a glass-topped bedside table seem to accentuate the worst qualities. Secondly, the output isn't a million miles away from what you'd get from the majority of iPod speaker docks in the sub-£100 price range.
Admittedly with the EOS system you can assume that at least some of the additional £150 cost is due to the wireless functionality and the additional speaker unit. Remember, the Altec Lansing Octiv-Air might have delivered a stronger audio performance, but you did get just the one wireless speaker for your cash, with nothing built in to the dock.
All the same - and those two points notwithstanding - a lot depends on how much multi-room audio and wireless convenience mean to you. Much as I like being able to lug the lightweight wireless unit from room to room or the thought of adding additional speakers for my office or bedroom, at £250 we're only talking decent rather than great value for money. More to the point, there are portable iPod speaker docks for less that offer better sound quality, and you could easily buy two for the same sort of money. If you want to create a cheap, reasonable sounding iPod-driven multi-room system and you're not bothered about ultimate sound quality then the core system is a decent buy, and for ease of setup and use the EOS wireless system is beyond reproach. Just be aware that you could get better sounding music for your cash.
A well-conceived, flexible and upgradable iPod wireless sound system, but the trade-off is that audio quality is slightly second-rate.