I've got no personal experience of the Super.Fi so I'm not qualified to comment on its sound quality, but I was put off by reports saying it can be uncomfortable and difficult to get to stay in your ears. That's not the case for everybody, but I know that I hate it when I can't get a good fit and have to keep fiddling, so didn't want to take the risk with them.
The Denons, which I do have, is a superb earphonephone and fantastic value for money.
If you're thinking of getting the Denon AH-C751 would you also consider the AH-C700? ... it's the exact same earphone, but it has a 1.2 metre cable rather than a short cable with an extension, and it doesn't come with a pouch to put the headphones in. The sound, according to info I've read in this forum, is supposed to be identical.
I prefer not having an extension cable, as it just adds extra unnecessary weight, so I went for the AH-C700, which can be bought for just £60 from iheadphones.co.uk
They also have the AH-C751, if you really want the cable extension and carry case, for about £80 in Silver or £90 in Black ... but even though that's still a really good price I don't think the extra £20 - £30 is worth it for an extension cable and pouch ... they sound the same anyway.
The only negatives I can think off with the Denons are that they are canalphones rather than IEMs so you don't get quite as much isolation as you might do with some other earphones that go deeper into the ear canal, but I find them adequate and quite comfy.
The fact you mention £100 makes me think that you must be in the UK rather the the US, so I think iheadphones.co.uk is the cheapest retailer you'll find for the Denon's if you choose to go for them ...
Denon AH-C700 Black | SALE Now On!
Denon AH-C751 Silver | SALE Now On!
Denon AH-C751 Black | SALE Now On!
Good luck with whatever you choose.