You can't connect your speakers like that. Optical audio cables transmit digital signals, which need to be decoded (usually) and converted to analog before the signal can be amplified and sent to the speakers. Your Bose speakers do not have digital to analog converters, meaning they can't accept a digital input signal. They will only work with analog audio (ie red and white cables or 3.5mm headphone plug). So basically you have them hooked up correctly.
The optical to 3.5mm cables that you refer to are primarily designed for use with computers. Many computers use a 3.5mm jack that outputs both analog audio and digital optical signals. Those cables won't work with your speakers for the reasons stated above.