The "morph" you're describing is known as (both) spectral cross-modulation, and spectral convolution.
From what i've read in your question, I gather you're interested in essentially crossfading the two sounds together, but in the frequency domain not the time domain?
If that's indeed the case then there are a few ways to go about doing this. you can either create a patch in max 6/7 using the pfft~ object, which can get a little tricky, seeing as you'll need to learn about the Fourier Transform. You don't need to necessarily know the hard math behind it, but understand what it does, and how to properly utilize windowing and bins in the context of MSP to get the sound you're after. then it's just a matter of loading the two samples together and using a UI object (like a slider) to morph them together.
That's the simple version. If you've got a few grand to spend, get a Pacarana from Symbolic sounds - and you'll have access to what they refer to as "Tau Morphing". Essentially the same thing - but it's in real-time, and incredibly high-detail.
That's what happens when you spend 3k+ on a box with like 16 multicore CPUs in it dedicated to audio though.
Spectral convolution would work if you played with it enough, but the reality is you're looking at a lot of resampling, using a convolution reverb on the source sound - with the other sound loaded into a good convolution reverb program.
I'll tell you now. don't bother. it's a total crapshoot.
If you're unfamiliar with DSP, and you don't have the cash laying around for a Kyma Pacarana, then chances are you'll have to do this by hand, with a LOT of resampling.
The last option, which just sprang to mind, is Kontakt. It has a processing filter in it called an "AET Morph". (Authentic Expression Technology... lol fancy phrase for short term Fourier transform). you can use an AET filter, analyze a source sound, and apply the phase characteristics to another sound. Other than KSP scripting your own instruments from scratch, this is as close to Voodoo and black magic you can get in Kontakt - it would take a good few pages to walk you through the process, and most people just don't understand what their doing. Not because they're idiots or anything - it's just not very straightforward unless you understand the basic concepts behind it (Fourier Transform).
I can't afford a Pacarana, so until then, I process my cross-modulations offline in max.
do it by hand. pitch shifting, audio editing, formant shifting, etc. these are the kind of things that just take a good day of getting your hands dirty (after spending a good week reading about the process and not getting it day after day, and feeling like a moron!).
best of luck -
Aaron
