Hi there
Just my 2 cents worth, the sound qulity is the sum of your components and how they integrate with each other.
You have purchased the equipment and your are not currently happy with the sound delivered.
If you mainly listen to music avoid if you can satelite speaker set ups as general rule of thumb, but you have already purchased them, so for the time lets stick with them, you have done the right thing by trying the satelite with your previous hifi set up and have comented that they sound a lot better.
Now the problem could be either the amplifier or the source playing the CD, since you mention that you are using a cheap ASDA dvd player as your audio source, I would be inclined to connect it to AIWA midi system and try it out ( I asume the your midi hifi must have some for of aux input ) I am almost certain you will find that your music will sound worse, but in doing so you will confirm one way or another this theory.
Since you have returned your panasonic amp you no longer have the posibility of trying the set up the other way around until your replacement receiver amp arrives, when it does, try out your music with asda dvd player and with your mide system as a source and in doing so you will know for def if the cheap and cheerfull dvd is the source of you lack of sound quality.
Most people who listen to music mainly either buy expensive DVD player that sounds good with music or buy a separate CD player for music playback, although there are some reasonably priced DVD player that sound good with music, general connsensus for example is the LIMIT 900 which apparently gives a really good sound with CD playback. (check the DVD players forum for more info )
You may also want to invest on a pair of decent speakers to use as you main stereo, wether they are floor standers or smaller units on stands will depend on you budget and size of the room and keep the remaining satelites for 5.1 movies.The amplifier you have chosen does not have a speaker selection swicht a/b, but whatever you do, please audition before spending anymore money, find a retailer that will let you return the speakers if you are not happy with and exchange them or refund if yout not satisfied after an agreed trial period.
Hope this helps