I'm studying piano with a Casio PX330. Sound (ie. classic piano) seems to me good despite some bad reviews.
I would like to connect some active speakers now, because Casio speakers are of course small. Can anyone give me some advice on the matter ?? Thanks

Here is what I wrote the last time someone asked this. But read what you wrote, you are on the right track. You say the speakers are "to small". What I've found is that physical size is the best predictor of how well a set of speakers will work for use with a digital piano.
Look at this thread.

Also, why do you say "active" do they really need to be?

I made some test connecting both speakers only and a hi-fi system to the line out of the Casio Px330. I think that sound level at the Casio keyboard line-out is very low because speakers only gave me sound low. Even with the amplifier (Casio line-out to the amplifier aux input)I had to raise volume control high. Anyway Px330 sounded better than with speaker only.
Unfortunately I cannot use my hi-fi amplifier so I thought to active speakers.

I use a set of Logitech 2.1 speakers. Comes with a subwoofer. I think they are fantastic for the money and and the volume can rattle my house if I wanted to jack it up that high.

I'm using one of these. It's OK for a small room but for a larger space I'd use two of the same amps, one for left and one for right.
Audiosource AMP100
It's a 50 WPC amp but in mono bridged mode you get 150W so with two you get 150 WPC. Good quality and very simple no-frills amp. Cost is about $100.

piRround, do you refer to Logitech 2.1 z2300 ?

Yes, that's it.