I want to run multiple instances of 2.6. I thought it was supposed to be as easy as opening it twice. When I open the second instance it just replaces the first. What’s going on?
What’s your platform/OS?
For Windows, it should be as simple as you suggest, it’s what I’m doing (WinXP)
For OSX, I think you need to copy the entire application. That has worked for me in the past.
For Linux, I’m not sure 
Works fine under linux, although when using ALSA it works like ASIO (only one program can access one card). Just tested on win7 too, you can launch multiple instances.
This depends on your soundcard drive, it is not a limitation os ASIO! (Unsure about ALSA.) Have had multiple programs using ASIO on my RME, using same virtual output to same physical output, many times.
EDIT: RME, not RMA. Obviously I’ve been sending too much faulty equipment back for repair recetnly 
Under Linux multiple Renoise instances works very well using Jack. Actually you can route audio between them, mix them, process with external programs or whatever else. Only limitation is imagination with Linux/Jack. 
Same applies to ALSA, some cards can be opened by multiple programs, some can’t.