Whew! Let's see if I can answer both of your questions in a clear fashion without confusing everyone.

First, no way, IMHO, can a box mix compete with a scratch cake, VKL. You just need to learn the basics of scratch cake making, that's all. If I lived in Indiana I'd come over and be happy to give you a lesson - it's not hard, just the details are important. Carol was right about why your cakes are coming out tough - you are beating them too long. And you need to use the paddle attachment, not the whisk. when you are mixing the dry ingredients in, switch to the paddle attachment and mix on low speed. This will also help decrease your chances of a tough cake. Be gentle with it! Think of it this way - when you are making a "quick bread", all recipes say to mix "just until incorporated", right? Its the same for cakes. Cakes are, for most intents and purposes, not very different from quick breads. Thats why you whip the eggs pretty well, add other stuff, then add the dry ingredients in stages and mix on low. You do not want to over mix. Try these tips:

1. First, sift your dry ingredients twice.
2. Switch to cake flour. I personally like King Arthur's Lady Guinevere cake flour, but really, any cake flour is fine.
3. When adding your dry and liquid ingredients, keep the mixer on low. Yes, it takes longer to incorporate, but so what?
4. DO NOT OVER BAKE!!! Tough lesson to learn, we are taught that when the cake shrinks away from the side of the pan, it's done. Wrong; it's over done. When the cake first BEGINS to come away, a mere sliver, and you gently touch the middle of the cake with your finger and it feels slightly springy, it's done. Pull it out and set it on a rack to cool, in the pan.
5. Try a chiffon cake first. They are pretty sturdy. Pick up a copy of the Cake Bible by Rose Levy Berenbaum. Great book. In chiffon, you will mix the yolks, liquid and dry together, then fold in the stiffly beaten whites until completely incorporated, then bake.

VKL, remember: cooking is an art - baking is a science. This means that you must be much more precise in baking than in cooking. The slightest thing can screw up a cake, and sometimes it's difficult to figure out. You just need to read about cakes and what makes them work and what doesn't. Get the Cake Bible. Once you've got batter cakes down, try a genoise cake. My favorite. Beautiful texture.

You said your cakes are sometimes eggy? Either you have too much egg in it, or the eggs aren't fully incorporated into the batter. That's why most recipes say to add eggs one at a time, incorporated each one fully before adding the next.

Carol, French buttercream. In most books it is called french buttercream. It's just that Alice Medrich doesn't consider that there is any other kind of buttercream (one of the reasons I love that woman!!!) and so just lists it as "buttercream". French is made by first warming egg yolks and white sugar together until very warm. I do this by taking my mixer bowl and setting it in a pan of very hot water, then mixing the eggs and sugar around with my bare, very clean hand until it almost feels hot. Very important to keep mixing, or the yolks will scramble. Once you have that, you put it on the mixer with the whip attachment and beat at med-high speed until it's very lemony, then go to high speed and beat until it's a stage called au ribbon - ribbon stage. When you lift the whisk the batter forms a ribbon and doesn't sink immediately into the main body of the batter. The volume will increase 3 or 4 times. It will be extremely light in color. Meanwhile, you will have been preparing sugar syrup to the low end of the softball stage. With the mixer on medium speed and having switched to the paddle attachment, you will slowly, very slowly pour the sugar syrup right next to the beater - not on the beater, not down the side of the bowl, or you will end up with clumps of sugar in the bottom of the bowl and you will have to throw it out and start over. Next to the beater. Once all the syrup is in, switch to high speed and whip until totally and completely cool. When that is done, you will take very cold butter chunks and start adding them a little at a time, having now switched back to the whisk attachment. If the yolks aren't completely cool, the butter will melt and you will have a big gloppy mess. When all the butter is incorporated, take a big spoon, and eat it!!! Well, I guess you can put some on a cake if you must! Anyway, you can refrigerate it for a bit, and you will need a cool room to frost the cake. With all that butter and yolks this is a very soft icing.

If you need a recipe I can post one for you.

What are you doing in Jakarta? I'm very jealous. It's 23 degrees today here, and I've had about as much snow and ice as I can take for one winter!!!