Generally the only way you are going top trash a pair of studio monitors is if the line level out of the TI is going to go into you studio monitors un-attenuated - and thats assuming the gain control on the back of the monitors (if any) is also at -3dBfs or above, and that the monitors either have no limiter, or its not a full band limiter (for eg only protecting the bass drive unit).
If you can trash the monitors under other circumstances, then the chances are you were going to trash them one day anyway.
Personally I would *NEVER* stick my monitors directly into any digitally controlled synth (or quite alot of digital outboard) - so many of them have digital volume controls that can get reset to full level via a MIDI CC or some other means not directly under phsyical user control.
The only things I would plumb them into are devices where there is no way in hell anything other than me has control of the output level into the monitors. If you dont have that - then buy decent quality but cheap and minimal mixer or a monitor control box so that you have a hard gain control in line. (If you have golden ears and can tell the difference - go have a winge at whoever made it - they will probably hire you
)
If you take control of gain staging to your monitors back into your own hands - then no way in hell you can blow them up from raw line level digital crap somewhere in your system - unless you also do something stupid - for eg maxing master volume because your gain staging was hosed.
Also if you monitors have a gain trim on the back - can be worth dropping it down a little bit - to at least -3dBfs - thats generally enough to protect most from raw crap at max line levels from a digital source. It also helps to protect for all the usual studio mishaps - mics left on, forgetting to zero the levels on guitars when done with them, forgetting to zero master monitoring levels before messing with a patch bay etc...
Some things about the new software world encourage a complete lack of old-school studio discipline that came about to safe guard gear (usually when some poor bastard had blown the hell out of something rare and expensive
) - worth picking up some of those habits at least as even in the purest of software environments, you still have some hardware in the form of your monitoring chain... If nothing else - get into the habit of sensible gain staging and zeroing levels of unsused gear or before messing with audio connections (or powering gear on/off).