I got the BS5 for its aesthetics and nostalgia value.  I also got a Beo6.  Surprisingly, the Beo6 can be reset and, out of the box, will control the BS5 without further work.  Which saved my bacon because I proved utterly useless at programming even the most basic of functions: getting it to show the battery status without turning off your entire ML setup, which according to the Beoworld guide from 2011, generously written by a German user, is supposed to be elemental (!). I do not see why a BS4 wouldn’t work with your BS5, but I’d be surprised if there is a lot of integration.  In my case, I’ve ML’d my BS3000 to the the BS5, and I can’t say that they add much value to each other.  Sure, if I hit N.MUSIC on the Beo4, it starts the BS5.  And ditto if I depress CD on the Beo4: the BS5 stops, and the BS3000 starts playing a CD, for example. But that’s pretty much it.  The BS3000 does not display any N.MUSIC metadata from the BS5, even though it is able to, because that’s what it did, well over a decade ago, playing N.MUSIC from BeoLink PC2, via LinkPlayer software (alas!, RIP).  I’ll bet you dollars to donuts that the BS4 won’t either, though I would very much like to lose that bet. The BS5 works pretty much exactly like a giant, great-looking iPod would.  I would not recommend it as an incoming digital media player, at all.  You’d be able to hook up your WIIM Pro to it, and all it would display on that gorgeous screen is a detestable AUX IN sign in white letters right in the middle of it.

Thanks, that's very useful.  The BS5 is a lovely looking thing but it sounds like it would not be very integrated with my BS4.  It depends how cheap I can get one, I suppose!  I'll give it some thought. If I used WIIM Pro instead I would have to connect that into Aux In, then connect my phono stage into the Aux In on the WIIM Pro, then connect my Beogram to that.  That could work though, as the WIIM Pro switches to Aux Input automatically if it detects a signal. What I'd miss there is having a dedicated screen for digital music, which the BS5 would provide. One annoying thing though - the Beo4 does not seem to have 'L-A.Aux' available as an extra button, so I would not be able to select that source using my Beo4 on my Beolab 3500.  It has L-V.Aux but not L-A.Aux.  What a strange omission!