If you're using medium size tips, try the small double-flange tips that come with the RE-400 (I think they come pre-installed) as those have the most narrow bore. Those are kind of designed for a relatively shallow fit, but even if they're not the most comfortable, see if that makes a positive difference sound-wise to you...it should elevate the bass a bit due to the narrower opening. I will say tip rolling will only take you so far, but it's worth an investigation. Sony Hybrids are good to try too.
There are pretty neutral options out there that have bigger bass body, more lushness and more slam (relatively speaking) or I guess you can say different degres of neutral. For example, I own the Flux and it's not quite as refined as the RE-400 but it's definitely a more engaging, warmer listen and a more ideal choice for electronic in some cases (or for some preferences). The EPH-100 is actually pretty neutral, just with a bass boost in the lower registers...I never felt they were truly v-shaped, rather the bass/mids are relatively balanced with one another and the treble is smooth behind them (hence warm/smooth category in joker's writeup) so more of a natural downward slope. Some will find this a more natural presentation overall and more accurate, and I can definitely agree with that...it can paint a more realistic image in some genres. I personally have the RE-400 now primarily for vocals and acoustic tracks...it's a great all-arounder but on the more relaxed, less engaging side of that and is best suited for those types of music IMO, while not entirely lacking in others...it's all about the mids.
The measurement can be deceptive though comparing directly to those of the RE-400, but I can say there is audibly less sub-bass reverberance in the RE-400 even though it goes down low (similar to how some single/dual BA IEMs sound). The bass is pretty big and fun on the EPH-100 but without drowning out any other frequencies, as well presented forward bass should be (you don't want muddiness of course) and you can feel the bass (adds a sense of sub-bass realism). The RHAs are similar, with more of a downward slope so that they're warm with more forward sub-bass but also has a smooth signature overall. Joker's writeup on the MA750 has some comparison to the RE-400 so you can see where each pair's merits lie...I'd say that they're on par from a technical standpoint, with different presentations: http://theheadphonelist.com/headphone_review/rha-ma750-ma750i/ Same can be said from my (and his) assessment of the EPH-100...these are still not true 'basshead' levels of bass, but you get a better sense of proper bass presentation, at the cost of changing the FR slightly. This is one reason I encourage people to try out different things, because at least in my journey it's taken a few tries to find out what balance is best suited for me...and my favorite IEM to date is the BA200 but the RE-400 still has it's place in my collection.
of course! i'm just saying tip rolling is relatively cheap way to eq the sound and comfort welll cheaper than buying a new iem (where i get my stuff theres no refund soo your kinda stuck if you don't like it). plus you'll always need more tips right ?! =)