Mario,
It is true that KETRON, YAMAHA, KORG (& even TECHNICS) plus others each have different ways of 'interpreting/generating' harmony/techichord. Un/fortunately, there exists more than one way to harmonize notes and each company designs their boards to do such in various manners. Personally, of all the above, I like the way the TECHNICHORD/Harmonies are created on TECHNICS keyboards the best; warm, rich, and sounds are generally 'filling' to my ears.
To achieve this same effect on the KETRON products, there are some options you could follow.

Generally, the best warm sounds to have harmonies added to are the STRINGS, PADS etc. In this case, these are the voices with which you would want to add HARMONY to, rather than percussive voices (eg PIANO). The harmonizers (in most keyboards) have various harmony types that are perfect for some voices and not too good for others so you will have to play around and see which suits you.
On the SD1, you also have the option to choose what voice should be harmonized when using more than one voice (PROGRAMS). In this way you could have a layer of voices (PIANO, STRINGS, VIOLIN and PADS) called 'PIANOPAD' and have the harmony/technichord assinged to just the PAD voice. When you play this voice and turn the HARMONY on, you get harmonise (eg TRIO if selected) on just the PAD voice.
Harmony is generally a great feature but sometimes might 'weekend' the ear when over-used.
On your X1, to achieve such, use the 2ndVOICE feature and assign harmony to the 2nd voice. Now change the 2nd voice to some STRING, PAD, WARM etc voice while having your main voice as the hard, percussive voice.
Let me know what you think/if you need further assistance.

AJ

PS: In most of these keyboards, I believe most of the voices with harmonies have arleady been preassigned (with some having the capability to edit these assignments). The pre-assignments choosen by the YAMAHA & TECHNICS engineers in my opinon, seem to have an edge over the others - thank goodness, they are EDITABLE!