“Second cab, same as the first!”
(Second verse same as the first.)
Without going into crazy explanations about how wattage would be split between your 2 cabs, and a smaller cab could possibly get blown in the process without your overall volume increasing, and how some cabs are more efficient than others (not to mention speaker cone phase issues when... mixing drivers!!!!) - the very general rule is it’s best to get a second identical cab.
This places the cab higher up closer to your ears so you can hear it better, and both cabs getting equal power will now how equal output and equal power handling capabilities.
That said, if you want a smaller cab because the 410 is too much to lug around, consider that a different rig not to be used with your 410.
If you do want to use a smaller cab with your 410, and you don’t care about all the issues, then the best way is to get a separate power amp. If you get a 2 channel (stereo) power amp, you can adjust the levels for each cab. That way you can push either cab as hard as you want without affecting the other.
Or look in to getting 2 smaller cabs - say 1x15. Then use both at bigger gigs or just the single 15 at smaller gigs.
Your options are endless - but if you want to still use your current 410 cab, the very best idea would be to get a second identical one. (make sure they are both 8 ohm cabs!!)
If you really really really insist on pairing a smaller cab with your 410, then get a 16 ohm cab. They don’t really make 16 ohm cabs, but a 4 ohm cab with 2 speakers can usually be rewired as 16 ohms, or you can replace the speaker(s) that come in the cab to equal a 16 ohm load. (look up parallel vs series wiring for speakers)