Hi Jian,
as I mentioned, specifying the LODs or not makes no difference. If you look at the available LODs for those services, the one that I have enabled resampling for only goes down to 1:25,000 whereas the basemap goes to 1:2,500 so from what you have said it sounds like if I zoom in beyond 1:25,000 I should see the second tiled service albeit blurred. is that correct? If so what is stopping it from working that way for intermediate scale levels where the second service doesn't match the basemap?
Do you have an example that works as you have mentioned?
Cheers,