With cable length this long? As long as you have your hand on 75ohm connectors, you'll be fine. I sometimes have to try this unconventional way, by setting source component away from pre-pro ... so I do not have to remove the original source components off the AV rack.
Be sure you are using shielded video cable (RG59 or RG6).
Optical cable actually will need a signal booster device (lament term) after a certain distance (Bell guy in family).
If you decide go for custom made or premade, prepare to open you wallet. Plz disregard if money is no subect to you.
You should invest on a decent set of crimping tools; you might find it very handy if you are a frequent visitor here.
Find out how it would cost you custom vs premade. I'd like to have it made for you if you are willing to try this method. As long as you are covers the cost of materials and shipping.
On the splitter issue, try this site www.digitalconnection.com
As you've mentioned, there is only one (1) coax input on your receiver. In my opinion, I would rather to invest into a new receiver has two or more coax input than a splitter module. Which might as well cost you somewhere $150.00 - $200.00 for an additional input.