I'm playing MM6 again. I am in the process of getting Dark Magic Mastery for my party, and as a preliminary, I had just paid my first visit to Paradise Valley in order to clear the Titans and Hydras from in and around the village of Edenbrook. I was standing by the fountain in New Sorpigal, going through the routine process of enchanting my "take" after looting the cadavers in Edenbrook and was getting the usual low-level stuff – you know, Precious Ring of Cold Resistance +6, Death Mace Antique, Champion Sword of Force, and so on. I then came to a Titanic Trident, enchanted it as usual, doing absolutely nothing different from what I have done so many times in the past, and to my utter amazement I obtained a Titanic Trident of the Dragon!
In my 20 years or so of playing this game, I have never ever generated an object of such quality from the Enchant Item spell. The best one I remember from the past was a Helm of Mana. So there it is. The Enchant Item spell CAN generate high quality stuff. But from my experience, it's such a vanishingly rare occurrence that I'll probably die before it happens to me again!
For your interest, I was playing the v1.0 game installed from a copy of the MM6 Limited Edition that I bought new in 1998 on a bog-standard Toshiba Satellite Pro 4300 laptop of roughly the same vintage, running under Windows 98.