I have been repairing the SV8000 FTA receiver since they were first introduced.
A little about me before I comment.
Electronic design engineer. Electronic technician, contract assembly owner.
Over 50 years experience in the electronic field.
Designed and manufactured one of the very first C band consumer receivers.
Now for my comments.
As for a problem receiving the OTA channels. Make sure you start and end the scanning frequencies for VHF and UHF correctly. That is usually the problem.
it does have an excellent ATSC system and tuner in it.
Now for the Satellite tuner.
The Signal showing is totally a reference (I assume you really mean quality. The signal is the amount of NOISE in the system) and as nothing at all to indicate the quality or signal from one receiver to another.
That indication can easily change even from one 8000 to another due to the tolerance changes in the parts. So one manufacture to another is totally impossible to compare.
There is only one way to test between two receivers. You set both receivers to the same sat and channel.
Now you put an attenuator on the LNB line. (Must pass voltage) You increase the attenuation till the picture just drops out. The turn it back till it just comes back in.
Now switch the receivers without touching anything.
If you have a picture great if you do not the first receiver has better gain in the front end. If you do have a picture increase the attenuation till the picture just goes out and note the difference between the two receivers.
You will probably find out there is no difference at all.
Almost all sat tuners have the same specifications.
The RF coming from the LNBs are most of the time. Way more that a tuner needs.
The most important thing that you can do is tweak the dish. Use a meter. As you tighten the bolts it will change. You need excellent CLEAN connections. Water proof everything. Hope that put some light on the subject.