diff --git a/app/core/render_engine.py b/app/core/render_engine.py
index 502302e..2bdb4b4 100644
--- a/app/core/render_engine.py
+++ b/app/core/render_engine.py
@@ -24,19 +24,20 @@ SYS_SOUNDFONTS = [
 
 def _find_sf2_path(sf_id: str) -> str:
     clean_id = sf_id.replace("sf_", "") if sf_id.startswith("sf_") else sf_id
+    clean_lower = clean_id.lower()
+    sf_lower = sf_id.lower()
     for base_dir in [UPLOAD_SF_DIR, SYSTEM_SF_DIR]:
         if not os.path.isdir(base_dir):
             continue
         for fname in os.listdir(base_dir):
             fbase, fext = os.path.splitext(fname)
-            if fext.lower() in (".sf2", ".sf3") and (fbase == clean_id or fbase == sf_id):
+            if fext.lower() in (".sf2", ".sf3") and (fbase.lower() == clean_lower or fbase.lower() == sf_lower):
                 return os.path.join(base_dir, fname)
-    # Backward compat: static/soundfonts
     static_dir = os.path.join(settings.APP_DIR, "static", "soundfonts")
     if os.path.isdir(static_dir):
         for fname in os.listdir(static_dir):
             fbase, fext = os.path.splitext(fname)
-            if fext.lower() in (".sf2", ".sf3") and (fbase == clean_id or fbase == sf_id):
+            if fext.lower() in (".sf2", ".sf3") and (fbase.lower() == clean_lower or fbase.lower() == sf_lower):
                 return os.path.join(static_dir, fname)
     return ""
 
diff --git a/app/static/js/app.jsx b/app/static/js/app.jsx
index 18969c2..2954ef4 100644
--- a/app/static/js/app.jsx
+++ b/app/static/js/app.jsx
@@ -6130,8 +6130,11 @@ const serializeTracksList = (tracksList, secondsPerBar) => {
       instrument_id: t.instrumentId || null,
       instrument_program: t.instrumentProgram !== undefined ? t.instrumentProgram : null,
       instrument_name: t.instrumentName || null,
-      soundfont_bank: t.soundfont_bank !== undefined ? t.soundfont_bank : null,
-      soundfont_program: t.soundfont_program !== undefined ? t.soundfont_program : null,
+      instrument_source: t.instrument_source || (t.synth_engine ? t.synth_engine.type : null),
+      soundfont_id: t.soundfont_id || (t.synth_engine ? t.synth_engine.soundfont_id : null),
+      soundfont_bank: t.soundfont_bank !== undefined ? t.soundfont_bank : (t.synth_engine ? t.synth_engine.soundfont_bank : null),
+      soundfont_program: t.soundfont_program !== undefined ? t.soundfont_program : (t.synth_engine ? t.synth_engine.soundfont_program : null),
+      synth_engine: t.synth_engine || null,
       items: items
     };
   });
@@ -6199,8 +6202,11 @@ const deserializeTracksList = (schemaTracks, secondsPerBar, sectionStore) => {
       instrumentId: t.instrument_id || null,
       instrumentProgram: t.instrument_program !== null ? t.instrument_program : undefined,
       instrumentName: t.instrument_name || null,
+      instrument_source: t.instrument_source || null,
+      soundfont_id: t.soundfont_id || null,
       soundfont_bank: t.soundfont_bank !== null ? t.soundfont_bank : undefined,
-      soundfont_program: t.soundfont_program !== null ? t.soundfont_program : undefined
+      soundfont_program: t.soundfont_program !== null ? t.soundfont_program : undefined,
+      synth_engine: t.synth_engine || null
     };
   });
 };