If you're talking about SQ, the sound reproduced cannot be better than the CD or whatever source it is playing from. The advantage of high end head units is they usually have more features such as anti skip etc. They have a more sophisticated crossover etc. Most importantly, they do not manipulate the source by themselves. You have to force it to with crossovers etc. The data coming in is the data coming out. This can't always be said for lower end units. Sometimes they prematurely clip even the preouts etc. In your case, Alpine makes solid units. They might take out this or that feature on lower-end models, but they will keep the quality up high enough that it will not prematurely alter your signal to where you would notice it. All you did with that line driver is bring the voltage up to what it would have been on a higher end unit.
Edit: Could I have used "etc" ANY more? I submit that I could not.