Nothing wrong with the diamond 9.1s, for the price they are rather good speakers but having a quick look at the specs suggests a fairly low senstivity of around 85-85db, given you're running them off a micro system with about 30 watts and low current I'm not sure they are the best match.
They may well have a certain synergy, I don't have first hand expeince but I'd imagine a more sensitive speaker (say 90db+), not neccisarily a better speaker but a better match. Typically larger ported cabinets are more sensitive and you may well be suprised how mcuh imporvment you can get by taking some of the stress of the amp allowing a effortless sound with better control in the bass and less distortion.
Speakers are so personal but for example I've just sold my old B&W 602 which are farily large standmount speakers for under £150 and they sounded brilliant with a tiny Tripath amp on all of 8 watts, I tried my more compact Mission speakers and the same amp sturggled.
Good luck.