Sounds like you're well on track, but since you're basically back at the beginning, I thought I'd add two possibly helpful suggestions. Consider 1) Water-based polyurethane OR 2) an oil-based finish / polyurethane that can be hand-wiped on, such as Watco or Minwax Wipe-On Poly. Watco would be my preferred solution.
Option 1, water-based poly, is great for light-colored finishes or natural finishes, and it sounds like yours qualifies. (Water-base is not recommended over dark finishes, though it can work fine on them, especially the recent formulas.) Water-based polyurethane is very user-friendly. Since California outlawed oil-based poly a few years back, the technology behind water-based polys has really come into its own, and the product, which is now used on wood floors as often or more often than oil-based, is great and PLENTY tough enough for your project. Having used both on many wood-working projects, and inhaled too many fumes, I am almost a 100% water-based person now, with just a few exceptions (and your project may be one—see option 2). Water-based polys dry more quickly than oil-polys, they are easier to clean up, easier on the environment, and their toxicity levels make it acceptable to apply them at home, which I've even done in a spare room inside the house. Now, I live in Texas, where warm weather and ventilation are plentiful, and you may have a different situation precluding home app. But even in the shop, a good water-based poly will be easier to apply than oil-base, because it dries much more quickly allowing more rapid application of coats, and less waiting time. Minwax makes
good water-based poly coats, called Polycrylic, or get an expensive one at the local woodworking store. You can apply water-based poly directly over the minwax natural stain (or any of their stains). It's a good idea to use the minwax natural stain (or other light-colored stain) under the water-based poly, since the water-based finish is so clear it lends almost no tone to the wood. (Woodworkers sometimes add a few drops of amber coloration to water-based finishes, just to correct this.) By the way, if you're using oil-based urethanes and seeking a natural coloration, you don't need any stain—the oil finish will supply all the tone you need.
Option 2, wipe-on poly, also may lend itself to home application, depending on your set-up -- and perhaps this is the kind of product you used already, like Minwax's
Wipe-On Poly. This is just regular polyurethane thinned to a consistency so you can apply it by hand. It works great for many projects, basically any where you don't need the high level of protection desired for, say, a dining room table. I'd use it without hesitation for an entertainment center -- but only in a ventilated garage, not in my house, since there are fumes. Wipe-on polyurethanes (and other wipe-on urethane-based finishes, like most things marketed as "Tung Oil," which is generally a urethane finish cut with some tung oil) are generally easier to apply than brush on varnishes and urethanes, and so they are recommended for first-timers, and much appreciated by experienced finishers too. Another popular wipe-on finish is
Watco's natural danish oil. This is my favorite product for oak. Avoid the non-natural Watco colors, but the natural is essentially a very very thinned urethane varnish. It works great on oak. You get a natural, hand-rubbed look and feel (like their marketing materials say, actually) that's very nice -- in fact, this thin level of finish tends to look a lot nicer on oak than thicker film finishes. Film finishes on the thick pores of most oak can look pretty ugly.
Depending on your aesthetic tastes, this last idea may be the most important of all -- and may incline you toward option 2. Were I finishing an oak entertainment center, I'd go with several coats of Watco, since it's so easy to apply, or at most, a few thin coats of wipe-on poly. My own entertainment center is in fact finished in Watco natural, applied over a dark mahogany dye stain. The finish and color look great -- and so do the other pieces in our home finished with Watco. These were also pleasingly easy projects.
Hope this helps. Birdman.
