The Valveking VK112 is a decent amp, but is not without its shortcomings. The clean channel is great. I've heard it described as being similar to a classic Fender clean. I haven't played through many classic Fender amps, so I can't speak to the truth of that, but the clean is nice. The gain channel is another story entirely. In my opinion, the amount of gain to be had becomes too much, too quickly as the gain knob is turned up. It's far too easy to get a thin, noisy, fizzy sound that swallows up the dynamics and details of your playing. Then, when the gain gets turned down to try to get those dynamics and details back and reduce the noisy fizz, it's no longer enough gain for a thick heavy crunch. The volume boost doesn't do anything, and unless you're using vintage out-put pickups, the gain boost doesn't do anything either. Another thing to consider is that at 50W output, even that open-back 1x12 speaker is going to get rather loud, rather quickly. Loud can be good when performing live, but isn't so much for practice.
I have heard of people modifying their ValveKings with different vacuum tubes, different speakers, transformer upgrades and the like, and supposedly these modifications can drastically improve the sound. However, modifying an amp can be a rather expensive way to find your brutal heavy metal sound. The amp itself may only be $200-$300 used, but after a new set of vacuum tubes, a new speaker, a new set of transformers, and other modifications to the amp, you could very well have ended up spending $2000 or more on getting the amp to make the sound you want. That $2000 could have been spent on the purchase of an amp that had a sound you liked to begin with.
If you're set on getting a vacuum tube powered guitar amplifier for some brutal heavy metal distortion sounds, save your pennies, and keep an eye out for deals in your area. Look on Craigslist, used music gear shops, pawn shops and the like. When you think you have found a good deal, take your guitar and play it through that amp and listen, listen, listen to the sound you get. If you spend plenty of time carefully listening to the types of sounds you get through different amplifiers, you'll eventually find a sound you truly love, and that should be the amplifier you buy. You'll know the sound when you hear it. You'll have a huge grin on your face, you'll be feeling all bouncy and giggly and be thinking "Yes! THAT is MY sound." Don't commit to purchasing an amplifier until you have found one that produces that sound.
My recommendation: Keep the MG and multi-fx unit. Learn to tweak it until you get sounds out of it that are satisfying to you. Then work on your chops. Put all of your attention into practice and improving your technique, and save up your money for an amp purchase at a later date. For all I know you could already be an awesome guitar player, but heavy metal is a very technically demanding style to play, and that is part of where it's brutal awesomeness comes from. The better your playing technique, the easier it will be for you to play with a heavy, brutal sound. I'm assuming you're young, I'm guessing in your teens or maybe early 20s? If that's the case, you may very well have more free time on your hands than you realize. Practice for at least few hours every day and your playing will improve by leaps and bounds quickly. Lessons with a professional guitar teacher will help too. It'll take patience and self-discipline, but the results in the end are worth it. Then after a year or two of constant practice, I doubt your dad would be offended when you decide to purchase a high end amp with your own saved up money. And if he asks why you could very honestly tell him that your technique has improved, your style is changing, and you want an amplifier that will let you make the most of that.
