In my opinion, Keyboard amplifiers do a very poor job of properly replicating the sound of a piano, or in general, sounds one would expect from a keyboard. (Synth sounds, Brass, Piano, EP's, ect ect....) There is a reason for this too. I have had a Roland keyboard amp for many years, and for many years I have been dissatisfied with the sound. Now I am in no way bashing Roland keyboard amps, because I feel like they are a very good product, I just don't like the way they sound. Playing music through it leisurely it works great, but on the gig I am not satisfied.
So on to the reason why keyboards amps seem to fail at replicating the sound.... and the problem lies in the tweeter. Or more specifically, the 'Piezo driver.' The issue is not the Piezo itself, its the fact that they are not built to accommodate the grand range of a keyboard, and replicate high frequency sounds at high volumes. They fail, and we get that annoying distortion sound at high volumes in the upper registers of the keyboard. What keyboard amps really need, is what they place in all PA speakers, and that's a dedicated horn driver for the high end. Horns are able to replicate high frequency sounds under high power loads for years without failure. I've seen far more baskets being replaced and rarely if ever see a horn fail. So why do keyboard amps not add horn drivers? I cant answer that, but there are a few options out there. In my opinion they end up not worth the investment, because they are bulky, expensive, and weigh a ton. (One last note, I always am fighting the EQ on the keyboard amps, and I feel like keyboard amps have some weird mid scoop pre-programmed in that you are constantly trying to EQ out of your sound.... extremely frustrating.)
So enough babbling and now on to my recommendations.... Get a PA speaker. Passive speakers are a great alternative to keyboard amps BUT you have to carry around an amp and a mixer, and who wants to fool with all that? So that narrows it down to Powered speakers. And there I do have a few recommendations.
For the budget conscious out there, Electro Voice (EV) makes an amazing powered speaker, 1000watts (500program/continuous) that I personally use myself and I have to say that it really truly replicated the sound of my Nord Piano, and every time I use it I am extremely pleased with the resulting sound. The series I'm referring to is the ZLX series speakers, and they come in 12" and 15" variants. (ZLX12p/ZLX15p). They weigh in at 32lbs on the 12 inch and 38lbs on the 15 inch. It also has a cool back lit LCD panel for adjusting EQ and position of the speaker (Pole, Monitor, Wall) so it will throw the sound accordingly. I use the 12'' myself. They retail here in the states at $399 and $499 respectively.
For those who have a bit more money to spend, I would highly recommend the QSC K series speakers (K8, K10, K12.) This series doesn't come with a 15 inch variant, but when you hear the 12 you won't feel the need for a 15. Also whats nice about this series is that you get some more flexibility with the size of the speaker. For those who would like something smaller then 12 there's the 8" and 10" variants to choose from. All use the same 1000watt class D power amp, making them super efficient and very light weight. And the sound is scary good, and you have plenty of head room if you need to play a loud venue. Here in the states they are going for $699 for the 8, $749 for the 10, and $849 for the 12. Check them out.
Only down side to the powered speakers is you are relegated to two inputs. However these companies provide an aux input on all these series speakers which is great for hooking up your phone, ipod, mp3 player or whatever. But if you really need more inputs you can always roll with a small passive mixer, like the Peavey PV6 or a small Mackie 402 or 802 mixer, and honestly it really doesn't add much to your setup.
Hope this helps
