SEF urls

The difference in both URLs is the cid parameter.
In the first URL, the id 1083 is the id of the variant Cerato of your product.
In the second URL, the id 1035 is the id of your product.

I suppose that the second one is generated when you're displaying your listing of products while the second one is generated when you're displaying the cart which has a link to the variant selected (when you click on it, you'll see directly the product with the characteristic you set before adding the product to the cart). In that case, both as the same since your default variant is the Cerato one.

Why are you struggling with them ?
It's just normal.
If you're worried about the SEO, you shouldn't. The variants URLs will only be seen by your users and only the main product URL will be seen by the crawlers since they won't add products to the cart (it's not possible for them).

It does. We indeed made the SEFed URLs the same for both SEF systems.

The pathway, and cid information is necessary in the URL in order to have all the information on the page of the link. The name is for SEO.
It would eventually be possible to remove the controller and task from the URL and the pathway when empty. Even removing the rest would be possible I think.
You would have to modify the code of the files router.php and/or sef_ext.php in the folder components/com_hikashop for that.

I don't know about xmap.

Could you point out what kind of products are displayed on the site map which aren't on products listings ? That shouldn't be the case...

When you change a variant, the page does NOT refresh, so it's normal that the cid doesn't change.
The category_pathway is needed in the URLs. However, when its value is 0, it can be omitted as the result will be exactly the same. But if you have a value for it and you remove it, the breadcrumb won't be displayed properly.

The URL www.vintageleathersofas.com/Premium-Harv...8/category_pathway-0 IS SEFed. It's just not customized.
On HikaShop's end, all we do is ask joomla to convert the non SEFed URL and we have some code in the two files I mentioned above in order to tell the system how to SEF them.
The rest is handled by joomla AND/OR sh404SEF. So if the URL is not customized, it's because you didn't customize it or there is a problem in sh404SEF.

The category_pathway is not 0 when you previously clicked on a category name in a listing of categories on the main area and which then displayed the products below that category and then you clicked on a product there.
That tells the system where in the category tree you clicked on the product so that it can display the correct breadcrumb as otherwise, there would be cases where it would be impossible to know the category path which led to the product page. For example, if you have a product attached to the category "science fiction" and to the category "orwell". Then, you have a menu which displays a listing of the categories. First, the classification types categories: "by name", "by genre", "by what you want" and then, when clicking on a category, it display the sub categories and then the products... When you reach the product page of that product, without the category_pathway, you don't know if the user came from Menu->By name->Orwell or from Menu->By genre->science fiction. The category_pathway will contain the id of the category from where you clicked on the product so that the correct breadcrumb can be calculated.

It's possible that the plugin displays different URLs... Do you have some examples of URLs which are different from one another when SEF is deactivated because it's hard to talk without any information... ?

Indeed, the pathway is different. Then, maybe there is a but in the pathway calculation of the XMAP plugin... We'll have Eliot check that up on Monday (it's his stuff, not mine so I wouldn't know).

You might want to contact sh404SEF before starting your plugin.
I talked to the developer few weeks ago at the JoomlaDay in Lyon (France) and he told me that he had done something for HikaShop. I didn't hear back from him since then but that might just be what you're looking for.

You should already be able to do that with joomla 1.6.
There is a Redirect component that you can use in order to convert urls from the default ones to something you would like.