search for the pdf manual to get a reel sense of what they can and can not do.
Also, they are old, and every new Roland has 808/909 presets built in.
Or learn to use a synth, even better
to add on this,
I find roland has great sounds, but,
the parameters aren't that universal as when it comes to timing and alike.
I never owned a 808 or 909, but have a few roland product still in my setup,
like a juno-d, a td6v and an e36.
quality sounds, but the editing options could be more universal,
like time based parameters.
for example, I can set the decay time of my drumsounds, but only from -48 to +48.
No ****ing clou what that stands for, but there I have to rely on my ears and of course, highly important, the speakers I use to listen.
The td6v does come with a fair range of 808 and 909 preset sound that are tweak able.
At the end, you need to get the sound people know already and slightly change it, so it could be unique in it's own kind.
that's the real trick.
to sound original with familiar sounds.
that's why I do prefer synth sounds above all drumsamples.
once you have a good synthesizer to play with, there isn't much you can not create with it, even voices if you are smart enough and have a lot of time to get to know your own gear.