@wisciman99 -- Auxinput addressed the basic connection above, but since you’re new to this I’ll add some more detail in case it’s still a little confusing. The new integrated would be hooked directly to your front L/R speakers and your highest quality stereo source would also be routed into any line input on the integrated (let’s call it the "CD" input) -- really just as if it was a standalone 2-channel setup. Now, to incorporate the HT/Marantz into the system, everything stays exactly the same as it is now on the prepro (don’t even change the channel balance levels) except the front L/R RCA preamp outs from the Marantz get routed to the "HT Bypass" input on the integrated. Believe it or not, that’s it -- you’re done. And here’s the best part --to listen to stereo choose the "CD" input on the integrated, and to watch TV/movies just hit "HT Bypass" on the integrated. That’s it. Pushing just one button completely and seamlessly switches between 2-channel and multichannel, and ONLY the integrated is in the system for stereo (the Marantz is completely out of the chain). Best of both worlds. Almost hard to believe, right? I and many others on this site have done this with great success.
As for the Hegel (and I’d definitely choose the Hegel over the Halo Integrated), it really depends on your budget. The improvements in the 190 vs. the 160 seem to be more refinements than a complete overhaul from a sonic perspective, plus some added streaming/automation features that may or may not be important to you. Right now there’s an "as new" open box 160 available from a dealer for $1790 (maybe with full warranty) that I’d find pretty hard to pass up since you can probably sell it for little or no loss if for some reason you’re not thrilled with it. (If you’re interested in this I’d move quickly as it’ll likely go fast if it’s not gone already -- again, likely very little risk with this). The 190 is $2995 here, but whether it’s worth almost 70% more for the latest and greatest is up to you. Personally, I think you’ll be very happy if not thrilled with the improvements from the 160, so I’d do that and pocket the $1200 difference.
Sorry to be so long winded, but hope it helps.