im 90% sure the sound is not suffering due to ur HU...
its mostly the install + the speakers themselves...

ure running 2/3 ways speakers....dont expect too much out from them...

if u want to tramatically improve the sound...seal off the front <the back of it> with good dampening material..
and maybe get an active xover to adjust ur xover settings...
but then again...you can do improve so much cus ure running noncomp speakers...

btw...the s/n ratio doesnt really mean much when you dont know how theyre tested...
and i bet you cant even tell the differences a few dbs off from each other...