I agree with gk31ax -- but would like to add: if you really want to exploit the high quality a pair of BeoLab 4000 can deliver, then just using a minijack to speakers connection can easily be improved upon. The signal is sent to the AEX in digital form, and is then converted from Digital-to-Analog inside the AEX, through the in built DAC (Digital-to-Analog Converter). While an OK DAC, it's average, at best.
The AEX outputs an optical digital signal through the same minijack plug. This means that if you use a stand-alone DAC of better quality you can convert this optical signal to a better analog one, and then send that to your speakers. You get the same convenience, but significantly better sound, from bottom to top of the frequency range.
There are various stand-alone DACs on the market. I have a LAVRY DA10 that I can heartily recommend, as well as a Grace m902. You can find very acceptable DACs as low as a few hundred Euros. The ones I have cost about 800-1000. If you decide to go this route, then look for a DAC which is also equipped with a headphone amplifier to get the most out of the unit. (There are times when you don't want to wake others, but still want to listen to excellent quality sound).