Which amp under $500 to make HD600 sound like "M50"?

Well, that's the way I'm asking, with quotes on the M50 since I actually don't want my HD600 cans sound like the lesser M50s, but with some similar dynamics on bass/mids plus better soundstage while preserving the faster response on the HD600 (vs HD650 cans for example on the last aspect).

I have now an iBasso D12 amp, ATH-M50s and HD600 cans. I like the way the ATH-M50s sound on the iBasso now that both are burned, before burning the M50s were too sharp for my liking, now this cans have very fun dynamics on the bass lines and treble is smoother, i like this pair too much!

But, since I were using my M50s at work, I can stand this cans for long periods as they are closed and the bass lends to tire my ears after more than an hour. Then I decided to buy HD650 or HD600, after an audition I found the HD600 to be a better as an all around can while the HD650 was better for slow music as lounge, jazz, etc. Maybe the problem with this decision was I were using mainly music from my iBasso D12 and both cans were with stock cable, I'm sure with a good solid state amp and cable this cans will blown in every aspect HD600, but that's not the point now.

Now that the iBasso and HD600 are also burned I found this combination to be very sterile and flat, I can almost fall asleep lol! So I'm interested in getting an amp that can give life to this cans and more juice to get dynamic and fun bass, not punchy, a little more forward vocals, more soundstage and instrument separation and clearer treble, that's while I describe what I want, maybe the "ideal spec", but I don't to what to compare what I'm looking for but with the iBasso and the M50s.

I were thinking in a tube amp, I haven't heard one before, just solid state like the Lehmann BCL, it were nice, but I think I want something more musical.

I have considered AudioGD-FUN, TTVJ FET-A and Bottlehead Crack, but I think I still don't found the right choice. I have soldering skills and would go for something as higher as the FET-A amp if it's really worthy its price, its size is a big plus since I have to lock it down on a drawer at work after it's time to go home, that's also an inconvenient for a tube amp.

I'm planning to listen any kind of music, mainly latin music like salsa, lounge, rock, metal, jazz, classic, trance and pop like Donna Lewis, Jamiroquai, etc. I would also get the HD650 cable for the HD600 to help a little the final result. I'll be using the iBasso D12 as DAC for now or if there is a DAC/AMP combo that fits the deal then the better, but if there's an amp that's better than a combo for the price I'd rather go for just the amp by now.

Help me out any suggestion would be appreciated!

I cannot imagine switching the HD600 for something like Orthos or LCD-2 for example when I'll be driving it with the iBasso D12, which is the only amp I have by now. More over, it's hard for me to be buying too much gear, I had to use half of my income of 1 month to get the HD600.

I do like the M50s but as I said I want to give the HD600 some of its dynamics in bass through an amp. I enjoy more the warmer sound of the HD600 but would like to give it more dynamics, maybe I shouldn't had used the word M50.