This is a little dated but should shed some light on what I was told about my SP3 upgrade which is Ser No 112.
The cost of the HDMI upgrade is $1000.00 including a new upper chassis. The $3800.00 cost you mentioned also includes upgrading the mainboard, power supply board, and USB section to support DSD and high definition PCM via USB. This would get you the functional equivalent of a new SP3, but the warranty coverage would be limited to the new parts, and for 1 year. If upgrading the USB section isn’t critical for you, simply upgrading the HDMI board brings the unit to modern video spec, at a more reasonable cost.