[FrankHudson]

The E609 is often used hung by a mic cord draped over the top of a loud electric guitar amp. I can therefore tolerate a tremendously loud signal and not distort or damage itself. Yes, it has less gain than even a Shure SM57 (another rugged mic that can handle kissing the grill cloth of a loud electric guitar amp). Works great for that.

I actually tried using a E609 for vocals once. I'd just watched LCD Soundsystem, whose vocalist/front man uses a physically similar and somewhat related model Sennheiser model for his vocals. I handheld it and sang close to the mic's grill. Yes, I had to crank the gain on my interface even in this scenario, which is not what you are trying to do. It sort-of worked that way, super close micing, just capturing a vocal) but it's inherent sound didn't grab me.

The person at the store steered you wrong. The E609 isn't the mic to use.

The Focusrite interfaces work fine, but they don't have tons of gain in their mic preamps. They are fairly quiet (self noise) even if the gain is set to max however. And with modern digital recording at 24 bits you also don't need a bit fat signal to get a good recording. You should be OK with the Focusrite.

Those who already responded have suggested a condenser mic. They generally have a hotter signal and are more sensitive. In a distance micing scenario where you're trying to capture both a vocal and an acoustic they may be better. There are tons of inexpensive Asian-made condenser mics (some cheaper than the e609 or Shure SM57), for example the Audio-Tecnica AT2035. There are a great many others in this class, lots of things that other people might suggest.

Your original idea, the SM57 would have worked I'd think, even in a single, somewhat distant micing scenario. People knock the SM57 in that it's not a sensitive mic that picks up every nuance, but some vocals and some acoustic guitar can respond to it in favorable ways. I'm unsure about this. but I'm not certain that in typical home recording, untreated room for acoustic issues, that an condenser mic is always the best choice, but I'm no expert. I just know that in my untreated "studio B" (a bedroom home office) I use a dynamic vocal mic and an Irig Acoustic Stage clip-in acoustic guitar microphone.

Once you get your mic straightened out, you can move on to finding the best placement for the one mic to get your guitar and vocals balanced and to not pickup too much guitar boom and woof.

Hope any of this helps.