Corruption of scriptures

I have asked this question of many Muslims and have yet to get a logically consistent answer: Does the Quran say, or does it not, that the Bible has been corrupted? If so, in which verses is this found? A typical answer I have received when I ask is that "Allah only promised to protect the Quran. He never said he would guard the Bible too."

Yes. And?

If it is really true that no one can change the words of Allah, and that He sent down the Tawrat and Injil beforehand, uncorrupted, then how can Muslims contend that the Quran is the only perfectly preserved scripture just because it's the final one? Why would Allah fail to guard the previous scriptures if the Quran merely confirmed them? Or is it that the Quran does not confirm the earlier scriptures at all but instead contradicts them?

I can already hear a Muslim's answer to the last few questions: DO NOT QUESTION ALLAH.

Here you may find an argument that I have yet to see refuted. The gist:
Claims (verbatim):

The Quran is preserved.

God’s Revelations which preceded the Quran include the Torah, the Psalms, and the Gospel.
These Books make up a large portion of the Holy Bible.

The Quran, the Torah, the Psalms, and the Gospel are all the Word of Allah.

God's Word does not change.

The revelations that came before the Quran have become corrupted.

Although Muslims should believe that these previous Books are the genuine Revelations from God, they have to trust only the Quran as the final revelation and the only one that is preserved.

Those claims result in these premises, a dilemma for Muslims (verbatim):

1. The Quran, the Torah, the Psalms and the Gospel are all Allah’s Word.
2. The current Torah, Psalms and Gospel are corrupted.
3. The final word of Allah, the Quran is preserved.

1st Conclusion: Some of Allah’s Words are corrupted
2nd Conclusion: Some of Allah’s Words are preserved.

Read the rest for yourself, then comment and answer the questions I originally asked.