340 stands are too short for 170s. your best A/B would be to have the tweeters at the same height, or at least have 170s on taller stands.
it's not impossible to think that you like the 170s over the 340s. your first speaker was the 170, and you never forget your first love.
i preferred the 170s over a $1499 floor stander.
340s perform better in my large room, but they do not do well in this room which is quite small. i bring the 170s in here pretty often to listen to stereo music. at the same rate, i don't listen to stereo in my large room w/ the 170s. maybe it's just the best of both worlds. i can listen to either one depending on what i want to do. afterall, it's all about user preference.
and, it's OK to LOVE your 170s.