Internal DAC quality vs external DAC's

I would recommend keeping the digital components separate from the amplification.  

Internal for streamer "starters" or dCs. I see no reason for placing a DAC in an amp except for a sale to a "consolidator." Then one has increased complications for upgrade itis.

So without sounding like jerk, would someone please explain to me why a DAC should not be a part of an integrated box ?

I've read this multiple times but never with clarification as to why.

It's hard for me to believe that this is somehow an issue with the 4 products I've listed in my original post. 

@rockophile221 DACs have a relatively short life of 5 years or less, amps 10 years or more, streamers somewhere in-between.

Separate boxes are best to easily upgrade and elimination of RF and EMI interference.

There are major costs associated with separates, cable costs can be huge because you need additional interconnect, digital and power cables as appropriate for each individual component.

You pays your money and takes your choice.

the real, not so fun answer is it all depends

one box integrated units can be very good, but of course lack the flexibility to decouple the piece-parts - at the same time, they can be smart buys - for example an older gen hegel h160 has an older streamer/dac built in, but the preamp/amp section is still world class - so at $1700-1800 used now, the h160 will be a good buy even if you treat the dac as a throw-away...

streamer/dac combos have similar issues... dacs are maturing fast, lots of trickle down happening, oodles of connectivity options... streaming front end sand streamer protocols and connectivity formats may still have more room for development/format change over time (though many would argue that is rapidly stabilizing as well)

so it depends on the user, their desire for a la carte flexibility to change (at a real cost, as mentioned earlier), versus buy a good modern integrated unit, use a good music source - e.g. tidal or qobuz, and be ’one and done’, just enjoy the music with a minimum of clutter (and complexity and cabling and power supplies)...