heh heh. I LOVE THIS WORK. It's not work, it's PLAY!
Machtlos does not appear to have microfilmed church records, but Ronshausen does, AND some of them (1808-1812) are online. So this is far before your emigrating ancestor, but might be 1-2 generations back. If the town really is as small as it appears, there may have been only one or two Gernhardt families...
There's an index of sorts starting on Image 8 of 261 and there's reference to a Conrad Gernhard marrying 28 March (no year given) with a reference to page 12. Then there's reference to a Martha Elizabeth Gernhard born 10 Nov, ref to page 30.
So let's first go to page 12 for Conrad's marriage... Oh man... the pastor (or whoever) who kept these records was a wordy man. These are not easily formatted marriage records, but each marriage has a longggg narrative (this one is FOUR PAGES), and while I'm generally pretty good at deciphering the old German script, this guy's handwriting is a doozy... The marriage definitely took place in March, and it looks like it too place at 6pm... Conrad Gernhard (I think an age is provided), son of [another] Conrad Gernhard and Anna D.... [married] ____tt [later learn her first name is Martha] Elizabetha [UGH cannot make out her last name] of ___bach born... daughter of [get this:] Adam Schaub? and Elisabeth Brindal?? [it's really difficult to read]; the bride's age is also given, but I can't make it out. There's more narrative, reference to the parents (die eltern). The marriage record is FOUR PAGES long. What's lovely about it is that it includes the (MUCH easier to read) signature of Conrad Gernhardt -- two of them (likely father and son) as well as Adam Schaub, Heinrich Schaub and additional witnesses Conrad Schaub and Johannes Schaub. (Their signatures are FAR easier to read than the pastor's handwriting.)
Now on to page 30 for the birth of Martha. The father is definitely Conrad Gernhard, and he might be of Hernbach or Horenbach. The mother is identified as Martha Elisabetha, born Schaub (i.e., her maiden name was Schaub). The daughter born this day (which I cannot decipher) is another Martha Elisabetha. Names of "sponsors" (like Godparents) are also listed: Georg Wilhelm _____ and his age; Conrad Schaub, his age of Hoehnbach... Signatures of Conrad Gernhard and Conrad Schaub join that of the pastor.
"Deutschland, Hessen-Nassau, Personenstandsregister und Kirchenbücher 1701-1875," images, FamilySearch (https://familysearch.org/pal:/MM9.3.1/TH-1-159389-106995-60?cc=1768560&wc=M6N3-72W:137637101,137274602,137275602 : accessed 06 Jul 2014), Ronshausen > Evangelisch > Geburten, Heiraten, Tote 1808-1812 > image 25 of 261; (that's the birth; marriage was image 16) citing Stadtarchiv Marburg.
I'd say there's a good chance that Conrad and Martha Elisabeth (Schaub) Gernhardt might be the grandparents of your Adam Heinrich...
AND if you look at Google maps, there's a Hönbach very close to Machtlos. ;-)