Hello benny...
I own both and have for a while. First, as sling pointed out- What is your source? (laptop, ipod, dac, cdp etc...)...If you're using a laptop/pc, an external dac is the way to go.
In reference to the amps:
LDI+---Three families of tubes (EF95, EF91/EF92 & 408A). It's a hybrid amp. Great with Grados and low impedance cans.
Mapletree--- Tubes- 12B4A x2, 5751, 12AX7, 7025. Great with both low impedance and high impedance cans (two headphone outs, hi & lo)
I can honestly say that I love 'em both and don't see myself parting with either. In terms of tube rolling, the I+ is a lot of fun and lots of tubes are inexpensive. With the Mapletree I have settled on the 7025s and they are some great tubes and great sound indeed. However, prices tend to go up on them.
In reference to- "Will I get $600 of greater sound from the MAD ear+ or will the LD I+ make my ears as happy as my wallet? """
Well, that's a tough one because everything is subjective in this hobby. Both sound great, as long as your "chain" is in order. The MAD will give you more options for the future if you get high impedance cans, whereas the I+ is limited to low impedance (I don't go over 75ohm cans with it).
I don't like to advise folks on how to spend their $, because, again, subjectivity is a big issue. I will say that you can't go wrong with either and both will give you your money's worth.
If I was in your shoes and had 700 beans right now, I'd go for the Mapletree and give them RS1's some MAD love....However, if I had 150 beans right now and that was it, I'd jump on that I+ and enjoy it, roll some tubes and opamps and after a while if your curiosity gets the best of you, then you take it from there.
Some pics I took last year while I was moving some gear around---
Cheers