Petr:

I'm sure that sooner rather than later someone with more experience than me will hop in, but what occurs to me is:

You must verify that the needle and any hardware you utilize on the 78's will not harm the 78's and will get the best rendition from the Lps available. 78's were all monophonic and probably have the sound making parts of the record in a different place than more modern needles, equipped to pick up stereo or compatible mono recordings. So check out that you can safely pickup the sounds.

I think the idea of utilizing software to make up the difference in speed is feasible, but you should experiment with your software to make sure it can indeed do this.

I believe that some 'modern' turntables not only could play 33's but also 78's, and those would be the ones to check out, since you need an analog electric output from the turntable.