Impedance for 4 ohm and 6 ohm in parallel is 2.4 ohms, in series is 10 ohms.
A series connection is + from the amp to + of the first speaker, then - from first speaker to + of the second speaker, and - of second speaker to - on the amp. A parallel connection can be a separate cables to each speaker from the amp or connecting second speaker directly to the first. Both of your descriptions seem to imply parallel.
Series is the safest, but will likely not sound good, and parallel will likely be too low of an impedance load for the amp.
Is this second pair of speakers for the same or different room?
A series connection is + from the amp to + of the first speaker, then - from first speaker to + of the second speaker, and - of second speaker to - on the amp. A parallel connection can be a separate cables to each speaker from the amp or connecting second speaker directly to the first. Both of your descriptions seem to imply parallel.
Series is the safest, but will likely not sound good, and parallel will likely be too low of an impedance load for the amp.
Is this second pair of speakers for the same or different room?