Truth is, most peoples' home theater systems are FAR more powerful and louder than just about any arranger's built in speaker system...
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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
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) 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.