Yes, technically, you can access the amp's power amp through the effects loop. But, anyone who tells you that it's going to make your sound "good" is telling you nonsense. All you're doing is accessing the power tubes.... it'll certainly give you a warmer tone than using a crappy solid state power amp, but that's really all it's going to do. Don't forget the expression: "You can't polish a turd."
What you're talking about is the same type of thing people do when they record a bad guitar track (or any track). If you record a bad track - i.e. improperly placing micrphones, bad room acoustics, not good mics, bad sound coming out of the amp, etc - then NO amount of post processing, such as EQ, adding reverb/ chorus/ delay/ etc is going to fix that badly recorded track. If it sounds bad, IT'S BAD. You need to start with something good, then add to what you have.
Well, it's the same thing with playing live, too. If you have a bad sounding preamp, then you have a bad sounding preamp. No power amp (or power amp section from another amp) is going to make that preamp sound good. It might make it sound "better," but that's a best case scenario. I know it seems as if I'm being really critical of you and my apologies because I'm not trying to be!
It's just that I actually was a huge proponent of rack gear and I started realizing how terrible it sounds compared to real tube amps. At one point, I had a Digitech Twin Tube preamp, which I used into a solid state amp. It always sounded thin and like a fly in a bottle (BZZZZZ ZZZZZZZZ.... you know the sound). Then, I bought a Mesa 2:90 power amp and played the Digitech through that. You know what it did? Nothing, really. It basically just made the "BZZZZZZ ZZZZZZZ" fly in a bottle tone louder and deeper.
I really suggest just saving up for another amp. Don't waste your cash on this. Just my opinion.