Afaik you're correct and the later Kenwoods use the same additional files as 2xx5/3490 etc. I think the split screen JCV will work, just try it. Maybe you should look at this thread in case it applies to your unit too: [Only registered and activated users can see links. ].
Where and how did you buy the LM map subscription? If it's a download from Garmin I don't think it's refundable. You said 'card' though, so if you bought a gift card from Garmin you may be able to return it within 14 days for a full refund. Amazon is pretty good about refunds too.
As to buying another 2nd hand Garmin unit to use the LM subscription with, it must be a unit sold originally with NA mapping as OEM, that is a localised US/MX/CA unit. Because you've already got the 2595 to lift files from i'd just be looking to sell off the LM sub you bought if you haven't already invalidated it by trying to load it to the Kenwood and/or can't get a refund.