Yes, I also have been thinking about doing something that would require some kind of a Y cable. I want to bi-amp my fromt L/R speakers, using my multi-channel amp. But I need to get two cables to the power amp for the front left and tow cables for the front right. I was looking for a cable that would make a Y at the amp end. But I don't think anybody makes this.
I did find this, but don't know how good the audio quality would be preserved through it:
RCA- Y Takes the Place of a Cable Type "Y"
This Y-connector takes the place of a cable type "Y" which can be considerably more expensive to make if made with top quality wire and connectors. It has one male and two females. The insulator inside is Teflon which sets it apart from similar looking ones - most of which use Delrin or other inferior insulator materials. This connector is of the highest quality with no loss or degradation. It is beautifully machined and gold-plated. Ours look very much like those "Y" connectors offered by our competitors. However, all others we have examined are made of brass with gold plating on top. Brass which is only 67% copper is not a very good conductor of electricity and consequently there is a performance sacrifice. Ours are made of an alloy that is 90% copper and then plated with gold. (One hundred percent copper would be too soft for this purpose). The ten percent of tin added to the alloy gives it the required strength and hardness. Because it is mainly copper, it conducts electricity far better than those of our competitors. It is more costly to produce, but it is truly a premium "Y" connector. It is essential that a connection such as this be of the highest quality to ensure there is no comprise in performance of your system. We believe this is the best "Y" available.
Then, I could just connect two interconnects to it and to the amp channels to be used.