I'll +1 on Annihilator as being worth a look. The soundstage is not what I'd describe as massive, but then again I've never heard an IEM come close to the expansive "out of head" width you can get with open back headphones. I otherwise hear Anni's presentation to be close to what you're wanting. To my ears, excellent (yes, excellent) bass presentation in both quantity and quality, transparent yet full mids with good vocal focus if that's how the recording is mixed and a masterfully extended and present treble that's effortlessly smooth with nary a hint of metallic glare or harshness.The Watercooler seems like the most active thread, so I bet I'll get plenty of high quality recommendations here.
I've recently fallen in love with the HIFIMan HE1000 Stealth. I'm not a fan of bright headphones, but it walks the perfect line between warmth, transparency, and air. So now I'm looking for a high-end IEM which shares this balance. Huge soundstage, lots of detail and transparency, but in a laid-back sort of way, with utterly natural tonality. Vocals which are airy, but not thin, subtly organic, yet wonderfully vivid.
This is a balance of contradictions I thought impossible. Until I picked up the HEK Stealth, and found my new favorite signature. More than enough bass, but all the technical prowess I could ever dream of. I used to love warmer headphones, like the LCD-3F. But now that sounds veiled.
I'm still treble sensitive. Too bright and I'm out. It's a fine line, and I'm hoping you fine folk have some recommendations.
@MatW owns the HE1000 SE as well as "a few" TOTL IEMs so he may be able to offer some meaningful insight as to which IEMs closely match the tonality of the HEKSE / Stealth.