Salamun Alaikum,
Yes indeed, in my humble view, the Quran treats them as two separate categories and both need to be
married through
'wedlock' (nikaah) before any such intimacy as indicated in verse 23:5-6 can be established.
004:025“If any of you have not the means wherewith to WED (yankiha) free believing women, they may WED (lit: then (marry) from - famin) believing girls from among those whom your right hands possess: And God has full knowledge about your faith. Ye are one from another: WED them (fa'inkihunna) with the leave of their owners, and give them their dowers, according to what is reasonable: They should be chaste, not lustful, nor taking paramours: when they are taken in wedlock, if they fall into shame, their punishment is half that for free women. This (permission) is for those among you who fear sin; but it is better for you that ye practise self-restraint. And God is Oft-forgiving, Most Merciful.”024.032"And marry those (Arabic: wa-ankihu) among you who are single and those who are righteous among your male slaves and your female slaves; if they are needy, God will make them free from want out of His grace; and God is Ample-giving, Knowing"I have endeavoured to cover this topic in the following article. Please note in particular the section:
WHY DOES THE QURAN DISTINGUISH BETWEEN 'MARRIED WOMEN' AND 'RIGHT HANDS POSSESS' AND CLASSIFY THEM AS SEPARATE CATEGORIES?SEX WITH SLAVE GIRLShttp://quransmessage.com/articles/sex%20with%20slave%20girls%20FM3.htmI hope that helps, God willing.
Joseph.