ok this is gonna be looong, but ive seen this happen before so im gonna lay it down for anyone else in this situation--
the motif isnt weak man...i would concentrate on learning the sounds on it and also on your composition. the concensus (from whave i have seen) between the big three names are this...triton has the electronic sounds, fantom has a wide range of unique sounds and motif has the straight up middle ground concerning hip hop sounds. there are also guys in the fantomized forums talking about how they wish the sounds in their fantom were as fat and rich as the motif. i highly doubt sampletank is going to overshadow it...its not the quality of the sounds within the motif that is the issue...its how those sounds are getting to your computer that is the issue. i would save up and invest my money in a soundcard/interface that has an optical or digital in...that way the sounds can be transmitted from the motif directly, without having to worry about cables. one thing is, you might be using unbalanced cables to get from your motif to your setup...(i dont really know what your setup is and it would help more if i did)...if you have balanced outs on your motif, using unbalanced (the ones that look like guitar cables) cables can create almost a 50% drop in volume...definitely not peanuts... balanced cables are the cables with two rings around the plug as opposed ot one.
if you're looking for a good program to integrate into your setup, thats one thing. but i think that software and hardware heads will agree that a big reason they choose software vs. hardware is the workflow and what works best for them...they choose less based on what sounds better...and that switching methods this early in the game for you is unwise.
also, when people have commented on your stuff in the showcase, it isnt really the sound quality, per se, but the WAY it sounds, ya feel me? the way you program your drums, the patterns you use etc...i guaruntee if you have a way of getting your motif sounds into your computer with high quality cables and inputs, and you work on your programming of drums and patterns, you'll be fine. also, your patch selection is key. which patch you use for what part is key. even if you had a $400 soundset of horns, you still can't be using them for the main melody or the main structire of the song...you gotta be tasteful. also, listen to how your favorite producers use your favorite sounds...if its strings, are they a main component of the track or are they accents. horns- are they looped in one melody or more like spices. make your melodies more rich, with patches that can support them. you feel me? instead of a 4 bar loop of a melody where you just picked a trumped sound, try an 8 bar loop where the melody is a (insert something other than orchestra instruments here)...
you might have noticed me talking about orchestral instruments a lot...my opinion is this: the big time producers usually hire horn players, etc if they want a horn sound...what does this say? a) they are filthy rich and b) you need to be playing a damn cello to have it reallly sound like a cello if you are going to get intricate.
either start sampling or practice your composition...(i suggest both but thats me). a dope producer could make an entire track with maybe a sample of a hand smacking someones face, a boot stomping, and pitched static noises...i know you probly dont want to hear this but its not the sounds, its the use of them and it seems like in your case, the quality of the avenue by which the sounds get to the computer.
i hope this helps not just you but anyone in your situation (ive been in something similar when i was starting out)
peace