The Launchkey is plugged into my laptop with a USB and plays through the laptop speakers. The G7 needs external speakers - I have a separate set of Logitech speakers - Bass and two speakers. I can plug the Logitech speakers into my laptop via the headphone socket, but then I can't play the G7. If I plug the Logitech speakers into the G7 I can only play the Launchkey through my laptop speakers. I want to be able to play both keyboards through the Logitech speakers. Is this possible and if so, do I need an adaptor, and if so, can anyone tell me what type please?
Attach the speakers to the G7
Attach the Launchkey to your laptop
Run a cable from your laptop to the G7.
From the Fantom G7 manual; "If your device has a stereo mini-plug output, you can buy a mini-to-phono splitter and use phono-to-1/4” adaptors to connect the left and right sides to the Fantom-G inputs"
You then need to set your mix of analog to output level. Again, that's covered in the manual.
When you're playing the Launchkey, it's not actually creating any sounds on its own, but sending MIDI signals to the laptop which acts as a sound source. So you have two sound sources: the laptop and the Fantom.
So you have three options:
An external mixer which will take the input from both the laptop and Fantom and output them to your speakers. If you get a small keyboard amp, most have a simple mixer of at least two channels that would meet your needs fine.
Feed the output of the Fantom into the laptop, use a software mixer on the laptop to allow you to output both the laptop's sound output and your Fantom's sound through your choice of the internal speakers of your laptop or your external Logitech speakers
(I don't know if this is possible.) Some Roland gear has its own built in mixer capabilities. You might be able to connect the audio output of your laptop to an audio input of the Fantom and then have its output go to the external speakers.
Option 1 is the most flexible but 2 is most likely to be the cheapest option, depending on your hardware and software.