There is not a lot of info out there for the PK-232sc+ in regards to the K3s. There are a few good articles for using the PK-232 for FSK RTTY with the K3. The PK-232sc with its DSP filtering for RTTY and the fact it has a very quiet soundcard - similar to the Navigator, make it a great tool for digital modes - even with the K3s. I have not tested the noise floor of the K3s's soundcard, but I'm sure it is very good quality.
Anyhow, I like a challenge. I have a hand drawn schematic of the interface cables between the PK-232sc (or sc+) that I would like to post in the files section. This cable connects the soundcard, and the FSK port on the PK to the K3s. This cable also allows the use of the other modes native to the PK like CW, PACTOR, PACKET, etc. Also connecting a keying cable from the PK's CW port to the key jack on the K3s will allow the PK to send CW while the PK will activate the PTT line at the same time.
Using software like DXLabs WinWarbler or MMTY for RTTY will use the PK's great DSP filtering for RTTY reception AND use the PK's soundcard for reception at the same time. This works really well in poor conditions. The PK or the PC will always decode the signal.
Using the Pk requires some setting changes in the K3s like you would for any external soundcard. The Line out audio needs to be set to 40 or so for the PK to work FSK and traditional modes like PACTOR and CW. Line In can be set to match the the soundcard output and separate AFSK output on the PK. Having two outputs allows you to set the AFSK level for proper deviation if using the 2m module for packet (WinLink etc.) or another radio. The PK has 2 radio connections. This allows the soundcard output volume to be set independently to help with ALC control if needed. My K3s Line in achieves proper ALC at about 15 with the levels set on the PK. For RTTY, the data mode on the K3s is set to FSK D, 45bps. For CW, CW mode, and for soundcard modes (PSK, FT8, OLIVIA, etc.) DATA A. That's very brief, but I can help with other details if you need them.
I made a cable that works fine, but I'm not that great with construction anymore. Ham made Parts built one that looks and works great. I would add the cable drawing file to the files section but it's restricted - can someone show me how?