I bought a Marantz at Goodwill and now I have a few questions

Got a SR-18U Amp at Goodwill this afternoon. I know this is a highly outdated HT Amp but better than the Onkyo I have now (I think). I am looking for help on the best way to wire this behemoth. My main question is the best way to set up my turn table. I listen to vinyl 75% of the time. My Onkyo has a dedicated Phono port with a ground screw. How should I try this with the Marantz? I have a CD player which is easy but I also have bi wired Sonus Faber speakers and a powered subwoofer to move over as well. All opinions (including throw it out) are appreciated. Just thinking those 140Wpc could really make my room. 
The power amplifier alone in an 18U is a great piece.

Wire it up as a stereo power amplifier, if you can.

IIRC, the power amp has a pair of 56,000uf 71V caps, and using that and the massive transformer, for just ’stereo’ is, well, overkill. Tons of reserve power.

It’s so good that if someone asked me for advice, for a 125 wpc 5 channel power amp (parasound, adcom, etc), and they said they could get an 18U at a good price, then.... I’d advise them to try that, instead of a dedicated power amp. As it is a very well built power amp, all on it’s own. To try the 18u along with the other pure power amps.

The 18u may easily outclass your onkyo, sound quality wise, if you use the onkyo for stereo and phono use, and switch to the 18u for this.

the drawback to the 18u is the potential to have it shut down from some fault in other unused parts of the circuitry, besides the parts you want to use. But you are already running that risk with the onkyo.

So. I paid $50. Should I wire via TV/ect crap outputs for phono and ground with the 10+ ground screws that seem to be available? And then biwire my speakers without bananas and then do my sub via a different output? Sorry but new to this. Honestly Im glad to get a reply. I really appreciare it.
Use the "tape out" on your Onkyo into an aux input on the Marantz for phono use.
ok thanks. Ugh, so I would need both in my rack to make this work? I assume a basic phono pre Amp would be better and smaller? 
Yes, the inexpensive Project is an excellent sounding phono stage. The only thing lacking is an extra 0 in its price (for snob appeal)!
Great, thanks. I think the Onkyo will find space in one of my sons rooms. They tend to get most of my hand me downs.
That SR-18 was TOTL in 20002 and cost around $2K! You got a bargain for sure! Use and enjoy it as a 2-channel amp!
I appreciate your help. Any additional input in regards to the speakers/subwoofer? 
Keep the Sonus speakers for now. Bi-wiring IMO does nothing! If you can, run your sub using long rca ICs from the "sub out" jacks on the Marantz. 
The Schiit Audio Mani at $129 is another fine inexpensive phonostage. Has different gain settings.