Yes, I too feel good mastering and recording quality music is also important if you want to hear the difference in SQ improvement but the easiest is to grab 24/192 and above source files to test instead of having to remaster and down-sample to 16/44. However, I can tell you very confidently that there is quite a bit of difference between hi-res and 16/44. If you never believe in that, I strongly suggest you test it out for yourself. The easiest is to go grab one of free hi-res mastered file from 2L - the Nordic Sound website, e.g. Vivaldi: Recitative and Aria from Cantata RV 679, "Che giova il sospirar, povero core". Get the DXD 24/352.8 mastering version and then re-encode it to 16/44. I use dBpoweramp to do the re-encoding and A-B playback them on my AK240 -> 1plus2. Technically, AK240 will also automatically down-sample the 24/352.8 quality to 24/176.2 internally during playback. But even then I can already hear the difference between the two. THe hi-res version sounds more energetic and has a stronger presence to every musical note compared to the 16/44 version, similar to what you can detect when switching from low to higher gain on an amp or from single-ended to balanced out. 16/44 version also sounds softer and more veiled throughout the entire track. The overall musical tone of 16/44 is still there and is the same as the hi-res version, but every note is less refined/detailed and the music sounds less full-bodied and less enjoyable as compared to the high-res version. You can also try the comparison on the other tracks on 2L. Some will yield less/more difference than others. YMMV.
As you offered this as an opinion, I feel the need to add mine too.
Still, before I do so I want to ask how big of an improvement you hear going from 16/44 to dxd? Could you give a percentage figure? Say the improvement noticed when going from the Tralucent Silver to the Tralucent Silver&Gold cables is approximately 5% for reference...use that as a scale if you would.