Regarding the Dmitri -- it’s a good conditioner, I used to own one, but not in the same league as current models such as the 12UEF and the Denali. Also in my experience the Dmitri will not sound good with power amps if that is where you want to use it. If on the other hand you primarily want it for sources and get it 2nd hand (they are widely available) then it could work well. By the same token you can also get very good deals on second hand older models from SR and Shunyata as well ...
The Niagara is worth checking but substantially more expensive then the other two options -- I suspect all of these things cost more in Singapore where I think you are
In the US at least with the dealers I deal with they should be prepared to let you borrow the demo model and trial it at home, Bear in mind that with power components such as these it may take many days for them to settle -- every time I unplug my SR kit it takes at least 24-48 hours for the cables to settle in again (likely a result of the active shielding to reestablish). And of course unplugging and replugging your components is likely very awkward.
The Niagara is worth checking but substantially more expensive then the other two options -- I suspect all of these things cost more in Singapore where I think you are
In the US at least with the dealers I deal with they should be prepared to let you borrow the demo model and trial it at home, Bear in mind that with power components such as these it may take many days for them to settle -- every time I unplug my SR kit it takes at least 24-48 hours for the cables to settle in again (likely a result of the active shielding to reestablish). And of course unplugging and replugging your components is likely very awkward.