Tube preamp between Oppo 105 and Meridian G57 amp

I am presently using a Meridian G68 processor in between an Oppo 105 source and Meridian G57 and G55 amps. It has a great sound and I don't think there are any processors that sound any better (other than a Meridian 861). However, I was thinking of a tube preamp. I know that would give up the surround sound that makes the G68 sound so spacious. But a tube may be even more spacious. Any ideas/experiences?
I'm not a big Meridian fan, but they do make good theater preamps. I used to have one. I think it was an 861, and don't think there would be a need to get something better for theater. The best solution would probably be to get a good 2 channel preamp with a HT bypass. Doing it that way allows you to focus just on the preamp without buying a bunch of features you really don't need.
I know what you mean. I thought the sound quality would degrade by removing the G68 processor and connecting the Oppo player directly to the amps. Not so. While I prefer movies with the G68 processor, I prefer music without it. Maybe because the player's analog outputs are digitizes by G68. Or maybe because of the power supply.

The HT bypass makes a lot of sense. It is the solution I am leaning towards. Another solution is to connect the Oppo directly to the G57 stereo amp for front speakers and go through the G68 processor/G55 5-ch amp for surrounds. I have all these components.

My concern is to add another expensive component only to be disappointed. After all, adding a preamp is an option not a necessity. Because the Oppo has volume control, a good power supply, and a good DAC. Of course the goal of adding a preamp is to improve the sound. But couldn't adding a preamp make it sound worse? I am pretty happy with the Oppo sound overall. The improvements I would like are better defined bass and smoother midrange. A tube preamp may smoothen the sound. But if it weakens the bass I would not be happy.