Are separates going to sound twice as good? No. Will a system with a decent preamp and dedicated DAC sound better than most AVRs? Yes, noticeably. The most recent AVPs I've had in my main system were Marantz AV8801 (the flagship at the time) and now a Marantz AV7704.
My Modwright LS100 has substantially better sound quality and I'm using an Auralic Vega for my DAC.
The AVP just can't extract the same level of detail (or holds back some of the detail, however you want to look at it).
On the other hand, I added a Jolida Fusion to my bedroom system and I would not say it sounds substantially better than my Integra DHC-80.3, which sounds surprisingly good for 2 channel listening. I'm not sure if the Jolida just isn't all that great or the Integra is that good, but there's not the same night and day difference between those two units that there is between the Marantz and the Modwright.
My Modwright LS100 has substantially better sound quality and I'm using an Auralic Vega for my DAC.
The AVP just can't extract the same level of detail (or holds back some of the detail, however you want to look at it).
On the other hand, I added a Jolida Fusion to my bedroom system and I would not say it sounds substantially better than my Integra DHC-80.3, which sounds surprisingly good for 2 channel listening. I'm not sure if the Jolida just isn't all that great or the Integra is that good, but there's not the same night and day difference between those two units that there is between the Marantz and the Modwright.