Is it possible to connect turntables and mixer to Acoustic Wave Music System 2 through the Aux, and simultaneously play a backing CD so that both can be heard? Eg, scratching vinyl over a hip hop beats CD.

Yes.

A traditional turntable requires a preamp inline with it to PRE amplify the minute signal produced by it's cartridge. Most setero receivers and preamps have Phono connection and internal preamplification strictly for that purpose. Many mixers out there have a Phono section or two, too, so your mixer will determine what you can do with vinyl.

Some of the newer turntables come with selectable internal preamplification to solve the lack of it in modern equipment.

The mixer can send its output to the Aux input on the AWMS-2.

If you have only the internal CD player I don't think you will be able to do what you want. Reason: the AWMS-2 doesn't have a traditional Tape Monitor circuit which would allow its own internal program (including AM/FM) to exit to your mixer and come back in via the AUX. Selecting AUX disables its output. Thgis is to preevent a potential feedback loop. The AWMS wasn't designed for people who want or can control complexity in their listening.

If you have the external 5-CD changer or another CD source, you would be able to run all that through the mixer prior to its entry into the AWMS-2.

In short yes! You will need an RIAA equalising and mixing amplifier to connect between the turntable and Aux input of the music system as the signal from the turntable is very small compared to the normal input required by the Aux circuitry. You need a minimum of 2 stereo inputs - 1 for the turntable and 1 for the CD player. These can be readily obtained in most countries and you can find plenty on the net by search for DJ mixer and they cost anything from £25, $35 or E30 upwards. This will also allow you to record the resultant mix via the Aux output which you can record on tape or CD etc.