im lost man if nuendo is your host and mpc is your sequencer what are you useing fl for? Any way check your midi in each program is passes through make sure your instruments and tracks are set to the right midi channels.
Ive worked on both if you got the money go with the mpc and a sound module or keyboard good cheap sound modules id get 1 second hand off ebay or sumpn like a asr 10, proteus 2000, or you could always get a rack like the 3080 or sumpn.. If you think hardware is better for you it probably is.. and...
If you use alot of synth presets and stuff youll probably here alot you recognize but like strings,piano etc there not as noticeable like that..but yeah software sound better everyday..
another thing when sampling drums you run your turntable through the mixer and eq the drums as there coming in cut the highs boost the lows and over all volume....basically if its hard when you sample it its gonna hit hard in a beat...
because of the sounds they have. Synth sounds take less money to make then getting multisamples of live instruments... sonik synth has alot mini moog and stuff plus quite a bit of it is just tweaks of the other sounds..
Peace