This is the first post I have ever made on Audiogon, and I am not a tweaker whatsoever (I just changed speakers after 25 years when a great deal for KEFs became available). I look long term and buy used or new depending on the item. I have found the most difference in the phono section by far (arm, cartridge/phono stage and table in that order). I didn't realize how much improvement could be gotten from a separate phono stage (or head amp as we used to call them).
My integrated amp which is phenomenal (Plinius 8200MKII), has a built in phono stage which I thought was equal to the other parts, and until I got a MC cartridge (VanDenHul Special One) I never thought about it. When I got back into thinking about the hardware in the past year or so, after upgrading my Rega P5's arm to the one on the new P8 (the dealer sucked me down a rabbit hole) and finally upgrading the table itself, someone mentioned that although the Plinius phono section is good, I could get a big improvement with relatively few dollars spent (although relatively is a relative term).
Since I upgraded each part in incremental steps, the arm improvement blew me away, and although the table sounded better it was a very subtle improvement thought it has a couple nice features. I just got a Sutherland Insight phono stage a few weeks ago (lucky to find one used) and once again I was blown away. It was based on the recommendation of several dealers. I would have bought a new one if I didn't find the used one. The guy who sold it to me set it up for me based on the VHD specs. You can see I am not a tweaker.
Bottom line in this discussion, make sure to separate the phono stage first, then worry about the integrated/separates argument. I lean towards integrated for space and value, but like I said, I am not a tweaker or tube guy. For the hardware hobbyist - have fun with tubes, separates, mono blocks, sub woofers, etc. For music lovers who like to keep it simple and mostly listen to music while doing other things KISS.