When you try both on the splitter, is it always the same laser that goes out or the splitter port that goes out? How long are the cables? Can you describe the splitter cable (eg. is it a connector with two cables coming from it)?
I will assume you set the projector settings in QS to TTL. But to answer your question on running TTL and Analogue mod lasers together, if you set the projector settings to TTL it will work but the Analogue laser will only produce 7 colours the same as the TTL. If you make the setting Analogue, then you will get full colour from the Analogue laser but run the risk of getting sketchy output from the TTL laser when the input signals to RGB drop below the lowest voltage required to trigger the laser for that colour (typ 3.5-4v). Plus the colours will not match from both lasers (e.g. the signal to produce Orange from the Analogue laser will produce ether Red, Green, Yellow or nothing from the TTL as the Red and Green can only be full on or off).
I don't know enough about laser specifications to say whether 520nm is better/worse than any other (it is a darker green though). What I can say, it is not just the wavelength you need to consider but the type of laser that is producing it (DPSS or pure diode etc.) as this affects other factors like dot shape and power requirement to name but two. I'll leave this one to others with more knowledge on the subject
While it shouldn't matter as they are both using ILDA Standard connections, it has been reported that some manufacturers have changed the connector wiring which has subsequently prevented the use of their lasers with ones from other manufactures. I cannot say this is what you are experiencing, as the use of a splitter usually negates this due to not using the through connections. it still might be something to consider.
My last thoughts on this are that since the lasers work singularly but not connected together, it is possible the signal strength is being affected by being shared between the two lasers projectors. Again this is not supposed to be an issue with the ILDA Standard, but it could be one of the laser units is drawing too much from the signal, leaving little to nothing for the other unit to work with. Is there no chance you can beg, borrow (steal
) another laser unit to try to see if it is one of your units that is the problem?