No such thing as too much sub, it just means you it'll player cleaner and those frequencies easily, and peaks will sound great. I'm using a SVS SB Ultra 13 in a small room and it sounds FAB. Although in a smaller room I'd recommend a sealed box. So consider the BK XLS400 or similar
Modern movies have an insane amount of LFE so you need a great sub, I'd recommend a 12" driver minimum, 500W sealed, 300W ported.
"i Agree a 500watt Sub will sound awful in not a very big room"
That doesn't make sense. I'm using a 1000W sub with 13.5" driver, and amplifiers for the speakers totalling 1700W total for the 7 channels. Why would a powerful subwoofer that can play loud, and low sound bad? In fact what'll sound bad is a low powered subwoofer, with small drivers, or speakers with little drivers. 25mm for soundbars mean it'll sound pretty tinny with poor midrange. Those drivers cannot reproduce the low frequencies that are needed, at high spl with low distortion. I've got a Q Acoustics soundbar that goes behind the TV, it's not bad for the size and sub is pretty good considering the TV's own speakers, and provides a fair rumble, but no way can compare against full on speakers and larger sub.
"My Dali kubic one is 100watt and my room size is not very big if i push near the limit it doesn't sound as nice"
That means it doesn't have enough oomp, you've just contradicted yourself. It sounds like you need a better speaker system. That's a soundbar is it not? 48hz-22khz. And isn't going to play that loud. So you're missing a fair bit from low end, 28hz, or more.
