Let us know what do you think about the U-Clock. In my system the change was neglible - not worth the money for sure. I'm also running my Puccini direct, bypassing ARC Ref 3 preamp.
You can get cardas RCA->XLR adaptors, or you can get a ARC Balanced Line Driver - I have seen one for sale not too long time ago for $500 or so on AgoN. Both will work.
You can still perfectly integrate your stereo setup with HT, provided that the Meridain has pre-outs for front speakers.
Then you can get rid of ALL 3 speakers you hang on the wall (including the center chanel, since in your setup you can choose a phantom center channel and get away without one).
I used to have system like that.
I used a HT processor, which feed a subwoofer and rear chanels through a separate power amp, and the fronts through my stereo setup.
Mert - I have DP-700 at home right now. It sounds considerably better than the DP-78, which is no slutch either ! You should audition it yourself if you like the Accuphase house sound.
Funny thing Mert - I remember when I once told you, that the preamp section of MF integrated you were using is nowhere near as good as a dedicated pre. You didn't agree with me and yet ... you soon bought the Pass pre.
I told you the - good move, wrong pre. You did not agree with (again), but soon replaced it with Boulder.
Then I told you than MF DAC/CTD combination is medicore - you did not agree with me (as always) and yet ... very soon you changed it for a similarly priced Accu CDP.
So this time I'm gonna tell you nothing - hopefully that will allow you to stop changing the gaer and start enjoying the music. j/k
BTW - Accu 550 is a very good amp. I have had it at home. I think it may be a side move though - it will not give you the slam, dynamics and resoluton oy your current setup. It should sound much more natural though - it is on the warm side of neutral.