A B listening suggestions?

Often i wanna listen and compare two versions of a song, let s say for mastering i send a track to outboard gear and record it back on a track in ardour. toggling solo and mute buttons of course introduces some time of silence or playing back both tracks at the same time… i m looking for a function (like a bypass in effects), for comparing version A with version B with one button… I checked in audacity and ardour and I have no clue… how do you guys compare tracks?

You can create two buses A and B and send every single track to both buses. Add an insert (or any mastering processing you want) into track A. Leave B as-is or add a little delay to compensate for any additional latency caused by the processing in A.
Then, engage “exclusive solo” mode, i.e. pressing solo will unsolo any other channel. Now use the solo buttons in A and B for comparing.

Thanks for the suggestion nettings, will try that soon!

I should have been more precise: i m still on ardour2/mixbus: is there also the exclusive solo function? I couldnt find it in the preferences… thanks!