Yes, option#2 would definitely be the least expensive but it does nothing in terms of your desire to migrate away from using an A/V receiver and toward using separates. In my opinion, it actually complicates matters by using your existing A/V receiver to power all channels of a new A/V preamp component.
The main thing you'd be gaining with a using a new 4K compatible A/V preamp is 4K video processing similar to the 1080P video processing currently incorporated in your SC-07 A/V receiver.
If you're not overly concerned with having 4K video processing with a new 4K hdtv, however, there is a 5th option you should be aware of:
5. Buy a new 4K hdtv and keep your SC-07 A/V receiver. You should be able to connect the video directly to your new 4K hdtv and completely bypass any video signal being sent to your SC-07, since it's unable to process 4K video anyway. You would just connect the audio to your SC-07 and still retain your 7-9 channel surround sound.
If a company in the near future offers a new 4K video disc player that has the same functionality as the Oppo 205, then this would also be a worthwhile addition to your system in a few aspects:
1. It would likely include a 4K video processor that optimizes 4K picture quality as well as up-sample non 4K discs and video signals to 4K.
2. It would likely include an internal 7.1-9.1 channel audio surround sound processor with 7-9 channel audio outputs that can be connected directly to external amps.
Using a 4K video disc player with these features along with a combination of separate amps for 7-9 channels,would also allow you to complete a migration to separates and eliminate the need for your SC-07 A/V receiver.
This method would allow you to incorporate a 4K hdtv, a 4K video disc player and a switch to separates in stages as your budget allows. Just another option to consider but, unfortunately, it does rely on a company introducing a 4K video disc player with the required features I described.