I am not in this situation because the cables are long enough for my use.

However, it should be possible to extend the cable from the subwoofer to the left speaker with a simple RCA extension cable (male/female).
For the large cable from the right speaker to the subwoofer, it should also be possible with a D-SUB 15 extension cable.
Please note that the D-SUB15 extension cable must be 1:1, i.e. each pin of the male plug must be connected to the same pin on the female side (this is not the case with VGA extension cables, I think).

Example of a cinch extension cable:
Value chinch extension (5 m, Entry level, RCA)

Example of D-15 sub cable: (no equivalent found at digitec)
https://cablesondemand.com/15-pin-hd-...