Rambam writes in MT (Yesodei haTorah 8:1 & 8:3) that Israel heard the actual words of the aseres hadibros on par with Moshe.
In the Moreh (2:33) he writes that they only heard an undifferentiated hum but no distinct words as opposed to Moshe who heard the words clearly and related them to Israel.
Are they reconcilable?
R. Yosef Qafih in his commentary writes without elaboration on 8:1:
ואין זה סותר לעומק הדברים האמורים במו"נ ח"ב פ' לג
And this does not contradict the depth of the matter as brought down in MN Sec. 2, Ch. 33.
Presumably this is intended in consonance with his statement in comment 13 on H. Yesode ha-Torah 8:3 (H/T @Nahum):
הדברים אמורים כאן על דרך ההטפה אבל ברור בדעת רבנו שכל אחד שמע כפי רמתו, וכמשפט כל חזון, ועיין מו”נ ח’ב סוף פ' לב, ופ’ לג, שם הביא לשון חז"ל במכילתא שמות יט כט משה מחיצה בפני עצמה ואהרן מחיצה בפני עצמה.
The matters discussed here are conveyed by means of sermonizing, however it is clear that according to Rabbenu that each one heard according to his capacity, and each had a vision as adjudged. See MN Sec 2, end of Ch. 32 and Ch. 33, where the language of Hazal from Mekhiltah Ex. 19:29 is brought that Moses had is own partition and Aaron had his own partition.
R. Qafih explains that H. Yesode ha-Torah 8:1 utilizes an exaggerated sermonic style to communicate the idea, and accordingly it ought not be understood as contradicting MN 2:32-33 where the unique level of each individual dictated the quality of their respective prophetic experience.
R. Isaac Sheilat takes a similar tack and elaborates further (Haqdamoth haRambam leMishnah, pp. 70-71):
In the above wording of the Mishneh Torah, characterizing the prophetic stature of the “presence” [of the Israelites at Sinai], it discusses seeing with the eye and hearing with the ear, and about Moses receiving the divine utterance: “Moses Moses, go tell them such and such” (H. Yesode ha-Torah 8:1). It seems that the Rambam employed this language by means of "hahaqal" (i.e. with imprecision), akin to what he wrote in his introduction to his commentary on Heleq (end of paragraph 6): " And don't try to come after me concerning that which I've said in a shallow unelaborated way about matters that men of wisdom grasp, for I have made the lesson easier so that those without any prior instruction in these exalted matters could understand.'' For in MN (Sec. 2, Ch. 33) the Rambam explains that the great voice that the Israelites heard at Sinai - the words were undifferentiated. And in another place in the MN (Sec. 1, Ch. 46) he wrote: “You'll find that the Hebrew language substitutes the apprehension made by one sense for that made by another... in conformity with this it is said, ‘and all the people saw the sounds’ (Ex. 20:15) although this station also constituted a vision of prophecy, as is well known and universally admitted in our community.” Which is to say: the language of “seeing the sounds” hints to an apprehension that is not sense-based, but rather is prophetic. And further (Sec. 2, Ch. 33): “The true reality of that apprehension and its modality are quite hidden from us, for nothing like it happened before and will not happen after.” The fundament of the matter here is to emphasize the sense of certainty of the divine revelation that all Israel merited at Mount Sinai, which establishes the belief in the prophecy of Moses with absolute certainty.
R. Sheilat here indicates that the language employed in H. Yesode ha-Torah 8:1 utilizes imprecise language in service of the overarching goal of conveying to the reader the weight of the Israelite experience, i.e. that trust in Mosaic prophecy was impressed upon them by the Sinaitic revelation. It is not intended to accurately describe the nuances of the prophetic experience which MN Sec. 2, Ch. 32-33 explain in greater detail.
If I come across any other explanations I'll update.
