KT-88, I’ve found Gold Lion warmer vs Shuguang Nature and Treasure. Have a pair of KR Audio 300B, absolutely superb. Never heard their KT 88, I would imagine thar are also superb, however they are pricey.
EL-34, I’ve found St Petersburg Svetlana the best, followed by Tesla and RFT. Never owned the Mullard xf2. Gold Lion KT 77s are very nice, a more modern clear, clean transparent sound than EL34.
Driver/Signal tubes, my favorite are NOS Tung Sol black bottle round plates, mouse ears and WGTA, followed by Sylvania GTA, then Raytheon WGT.
Never heard an SLI 80, but I run the tubes above in a Dennis Had Inspire KT 88 and a Cary 300B SEI. Similar construction since all designed by Dennis.