Truth is, most peoples' home theater systems are FAR more powerful and louder than just about any arranger's built in speaker system...
Only problem is you might be sitting some distance from it, which firstly will make you tend to play louder (not that that's a BAD thing
) and secondly will add a certain latency to what you are hearing (1 ms/ft roughly) so a big room may 'disconnect' you with your playing, a bit.
But, on the whole, if you never play your arranger louder than you would tend to play a CD through the same system, you should be alright.