Not to mention the KISS mode "delayed packet" issues with the KPC3+. Would be interesting to see if maybe the FTDI USB/serial layer has finally resolved that long standing bug with that model.
If the soundcard modem doesn't fit your APRS needs then I'd consider saving up just a few more $ and getting a SCS Tracker DSP TNC and have 5 modems (300bd HF Packet, Robust Packet, 1200bd, 9600bd, 19,200bd) in one well supported modern TNC. Super small TNC, low power requirements, and has built in headless tracker capabilities built in. Works FB with UI-View32 in KISS mode - powers our club's K4KPN-10 HF RPR APRS digi/gate and just runs and runs.
73
Jeff
WA4ZKO
Jeff - WA4ZKO