I'm looking for stories where the male MC is either a particularly amazing lover, or has some sort of amazing penis that the women love so much.
Similar to how the MC is in Six Times a Day.
Ideally harem/multiple women.
Any recommendations?
JRyter's stories that are tagged with "much sex". They are pretty much exactly what it sounds like you're looking for.
The MC in Deja Vu Ascendency fits that profile. He also has a harem. Three Square Meals by Tefler fits the profile as well.
https://storiesonline.net/s/57098/deja-vu-ascendancy
https://storiesonline.net/s/14679/three-square-meals