In recent years, the rapid proliferation of short video platforms among younger demographics has significantly amplified digital media’s function in propagating traditional music cultures. However, most studies predominantly target mainstream cultural phenomena or consumer behaviors, with comparatively scant focus devoted to music-centric traditional arts, such as saxophone culture. This study examines four major Chinese platforms: D1 Douyin (TikTok), D2 KuaiShou, D3 Bilibili, and D4 Rednote (Xiaohongshu), assessing their differential impacts on the dissemination of saxophone culture among youth. The research integrates Grounded Theory (a qualitative methodology employing open, axial, and selective coding) and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). We conducted 20 semi-structured interviews and distributed 563 questionnaires (555 valid, 98.6% response rate). Qualitative analysis produced a communication motivation model with four dimensions: cognitive understanding, emotional resonance, cultural identity, and behavioral intention, organized into three core themes and twelve subcategories. Using TOPSIS to rank platforms based on communication reach, content experience, and user engagement, Douyin led in overall effectiveness (closeness coefficient = 0.6323), owing to its algorithmic recommendations, immersive content, and social connectivity. KuaiShou demonstrated balanced performance, while Rednote (0.5510) and Bilibili (0.5350) excelled in cultural depth and aesthetic construction. Personality projection, social motivation, and immersive experience emerged as key drivers of youth engagement. This study provides a streamlined analytical framework and robust empirical evidence on the digital propagation of traditional music culture, offering practical recommendations for platform operators and cultural promoters in content planning, audience targeting, and platform selection.