UKJedi: Apologies for de-railing your thread with the plugin talk. Jeff and I are good buds and always seem to end up in great conversations during other peoples threads. LOL! Sorry about that.
In answer to your question, though additional synths like everyone has mentioned will definitely get you what you need, I feel that some of the advice Linear Phase gave you is also spot on and worth visiting. Though I wouldn't have totally advised you as he did (no offense Linear, honest!) he's on the right track in my opinion.
The word "warm" is the first mistake in my opinion. The reason being....this is one of those words that just means too many different things to too many different people. LOL! On one of the forums I frequent, you get this **** when you type "warm" because the site owner feels the word is just so mis-used, it becomes misleading to those in search of information.
Some people in Europe consider warm to mean "clean, with presence" while others like most of us in the USA consider the word to mean "balanced, without harsh high end, nice mids, a happy mixture of everything that isn't annoying to the ears".
So as you can see, the word can definitely give you different results. If clean and clear is your idea for warming, reduced mids and low mids with a touch of high end air will cure you. If you think of warm as *I* do, you want that edge taken off the high end. Part of my feelings here sort of cross with what Linear said.
Though I think the Pro Channel eq can deliver warmth, I disagree with "the gloss" option because it adds a little high end sheen to it. This to me is not the proper approach to warming something up. I also do not believe in saturators because they simply do not warm in the way *I* am used to. Saturators of the digital nature, distort more than they warm up the tonality. It's not like the old days when we ran a REAL tube pre-amp or something....these things (in my opinion) just totally fall short on what tube (or valve if you're from Europe) warmth is all about.
So, if something is cutting too much with high end and you want to warm it up, the first thing to do is to control the high end that is making it too abrasive. You will get high end from 2k to 6k. This is where you can remove harshness.
From 7k on up, you have what we call "the air frequencies". These add high end, but not in the form of harshness when used sparingly. So if you take off some of blatant high end from 2k to 6k, add some mids between 600 Hz and 900 Hz, those are the frequencies in MY opinion that will warm things up. If you need a little air so to speak, 10-12k is a really nice place to start.
Watch for low mids when trying to warm something up. With synths, the low mids and lows will walk on top of other instruments if you're not careful. You also have to keep in mind whether or not this instrument will be a focal point or a filler instrument. If it's a focal point, you can enhance it just about any way you want to allow it to shine. From there you'll need to conform the other instruments around it.
If it is a filler instrument....like pads that just enhance, you'll need to be careful of the mids and low end or you will easily get frequency masking. In this situation, I like to actually make my pads LESS warm so they will cut through the mix. In this case, my advice is the same as Linear's. We can use gloss, we can add a saturator for a little sizzle so the sound cuts through, we can boost a little more high end if needed....all this makes the pads cut through and in turn, you can keep them a little lower in the mix if you need to.
But honest when I tell you, a good eq is all you need to warm up a sound. It's just a matter of removing harsh highs and coming up with the right mids to accentuate the sound. If you find that you are working on the sound for a half hour or so, it's usually best to choose another sound as it shouldn't take that long to make it fit in the mix. The right sound source will always be the key in my opinion.
However, in the synth world, half of the fun is taking a sound that may not be right from the start and turning it into something completely different using filtering or aliasing etc. There are just so many variables here that it's tough to pinpoint. I can't tell you how many times I started out with a sound I hated for a pad that turned into something incredible while trying things within that sound patch. So definitely experiment, but know "when to say when" or you can sit there for weeks tweaking this stuff. LOL! Best of luck. :)
-Danny